All about potatoes.pdf - Vegetableipmasia.org

Authors
Editors
Contributors
Translation
Photography
Graphic design
Warsito Tantowijoyo (CIP)
Elske van de Fliert (FAO)
Handoko Widagdo (WE)
Jan Willem Ketelaar (FAO)
Gunawan
Junaedi
Sri Wahyuningsih
Basing Sembiring
Raja Ulung Sagala
Agustoni Tarigan
Eko Istiyanto
Mark Havard
Elske van de Fliert
Warsito Tantowijoyo
International Potato Center: Major Potato Diseases, Insects, and
Nematodes
Mukti Wibowo
Warsito Tantowijoyo
Elske van de Fliert
All about Potatoes
A Handbook to the Ecology and Integrated Management of Potato
International Potato Center (CIP-ESEAP Region) &
FAO Regional Vegetable IPM Program in South and Southeast Asia
In cooperation with:
Lembaga Pengembangan Teknologi Pedesaan
World Education
Food and Agriculture Organization
With technical and financial support from:
Food and Agriculture Organization of the United Nations
All rights reserved. Reproduction and dissemination of material in this handbook for educational or other
non-commercial purposes are authorized without any prior written permission from the copyright holders
provided the source is fully acknowledged. Reproduction of materials in this handbook for resale or
other commercial purposes is prohibited without written permission of the copyright holders. Application
for such permission should be addressed to: CTA, FAO Regional Vegetable IPM Programme, FAO-
RAP, Bangkok (vegetable-IPM@fao.org) and to CIP-ESEAP Regional Director (cip-bogor@cgiar.org)
For additional technical information on potato production and protection, please consult the following
website: www.cipotato.org. For additional information on vegetable production and protection, including
technical and training materials, please consult the following website: www.vegetableipmasia.org.

FOREWORD
FOREWORD
This handbook is an integral part of Integrated Pest Management Farmer Field
Schools for potato. Although a thorough understanding of potatoes will develop
through studies in Integrated Pest Management Farmer Field Schools, we hope this
handbook serves as a facilitation resource for facilitators of Integrated Pest
Management Farmer Field Schools. It intends, on the one hand, to give a broad
overview of the basic technical issues relating to potato cultivation, but, on the other
hand, broaden its users’ horizons into the areas of ecology, marketing and farmer
empowerment.
In this handbook we have tried to use language understandable to farmers,
purposely keeping material as simple but as thorough as possible. It opens with an
explanation about the principles of integrated pest management, then moves on to
technical production topics about potatoes. These cover cultivation techniques, the
ecology of pests and natural enemies, major potato pests and diseases, types of
natural enemies, and so on. This handbook is not like a book of fixed recipes. It
accentuates fundamental technical issues for potatoes, all of which still require
considerable development more specific to the conditions in each location. This
guide will become richer in scope if further trials are conducted under local
conditions.
The involvement of individuals with diverse backgrounds and experiences has given
this handbook on the ecology and integrated management of potato plants a very
different feel in terms of language style and content. The authors would like to thank
all those who have been so actively involved.
January 2006
We welcome your comments and suggestions. Please contact:
FAO Inter-Country Programme for IPM in Vegetables in South and Southeast Asia
c/o FAO Regional Office for Asia and the Pacific
A-25, Maliwan Mansion, 39 Phra Atit Road, 10200 Bangkok, Thailand
Email: vegetable-IPM@fao.org
For more information on vegetable IPM, including other training materials and ecological
production guides, please consult www.vegetableipmasia.org.
A HANDBOOK TO THE ECOLOGY AND INTEGRATED MANAGEMENT OF POTATO
i

HOW TO USE THIS MANUAL?
HOW TO USE THIS MANUAL?
Why this manuals?
Farmers, practitioners, non-governmental organizations and researchers have all
drawn on their experiences in developing this handbook to the ecology and
integrated management of the potato crop, which is enriched with information from
literature references.
Our objective in developing this guide was to provide a simple, yet complete picture
of an environmentally friendly approach to cultivating potatoes under tropical upland
conditions. Our ultimate hope is for potato-farming systems to change and become
healthier for farmers, their farming enterprises, the environment and consumers.
Healthy potato farming conditions will result in improved farming sustainability.
Who is it for?
This handbook is for use by facilitators of Integrated Pest Management Farmer Field
Schools (IPM FFS) who preferably have graduated from a season-long training of
trainers.
How can it be used?
This handbook forms the basis for the technical and ecological content of the potato
IPM FFS. The FFS is a farmer training methodology that through experiential
learning aims at enhancing an understanding of all aspects of the potato enterprise
among farmers. This does not mean the handbook cannot stand alone as a
reference on potato cultivation, but it will be more useful when considered the basis
for thoughts to be explored and enriched through the participatory learning processes
in potato IPM FFS. It should be noted that this handbook was developed under
tropical upland conditions in Indonesia. Although an effort was made to generalize its
content and make it applicable to other countries and environments, the user should
be cautious and always cross-check information gained from this handbook with
locally existing knowledge.
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ALL ABOUT POTATOES

TABLE OF CONTENTS
TABLE OF CONTENTS
FOREWORD __________________________________________________ i
HOW TO USE THIS MANUAL? __________________________________ ii
TABLE OF CONTENTS_________________________________________ iii
1. INTRODUCTION ___________________________________________ 1
1.1. Integrated pest management: an overview _____________________ 1
1.2. Potatoes: an overview______________________________________ 2
2. POTATO PLANT GROWTH AND DEVELOPMENT _______________ 3
2.1. The potato plant___________________________________________ 3
2.2. Potato plant growth ________________________________________ 3
2.3. Potato growth stages and vulnerability to pests and disease _____ 4
3. SOIL ____________________________________________________ 5
3.1. Soil ecology ______________________________________________ 5
3.1.1. Soil types 5
3.1.2. Soil acidity 6
3.1.3. Soil conservation 7
3.2. Soil fertility management ___________________________________ 7
3.2.1. Nutrients in the soil 7
3.2.2. Types and functions of nutrients 8
3.2.3. Testing soil to determine fertilizer needs 9
3.2.4. Organic fertilizers 10
3.2.5. Chemical fertilizers 12
3.2.6. How to apply fertilizer 13
3.2.7. Potato plant fertilizer requirements 15
4. SEED PREPARATION AND PRODUCTION ____________________ 17
4.1. Seed tubers and True Potato Seed __________________________ 17
4.2. Seed generations_________________________________________ 17
4.3. Criteria for healthy seed ___________________________________ 18
4.4. Seed selection ___________________________________________ 19
4.4.1. Positive and negative selection of parent stock 19
4.4.2. Sorting seed tubers 19
4.5. Treatment of seed tubers __________________________________ 20
4.6. Seed storage ____________________________________________ 20
4.6.1. Storage conditions 20
4.6.2. Pest and disease management during storage 21
4.7. Quality seed production ___________________________________ 21
5. CULTIVATION PRACTICES_________________________________ 23
5.1. Choice of location ________________________________________ 23
5.2. Potato varieties __________________________________________ 23
5.3. Field preparation _________________________________________ 23
5.3.1. Tilling the soil 23
5.3.2. Seedbed preparation 24
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TABLE OF CONTENTS
5.4. Planting_________________________________________________ 25
5.4.1. Planting time 25
5.4.2. Planting method 25
5.4.3. Intercropping 25
5.5. Hilling up and weeding ____________________________________ 26
5.6. Water management _______________________________________ 26
5.6.1. Irrigation systems 26
5.6.2. Watering 27
5.6.3. Water management and water-borne diseases 27
5.7. Crop rotation ____________________________________________ 27
6. INSECT ECOLOGY________________________________________ 29
6.1. Introduction _____________________________________________ 29
6.2. Insect anatomy___________________________________________ 29
6.3. Insect life cycle __________________________________________ 30
6.4. Insect pests _____________________________________________ 30
6.5. Beneficial insects ________________________________________ 32
6.6. Pest management ________________________________________ 33
6.6.1. Biological control 33
6.6.2. Mechanical control 34
6.6.3. Chemical control 35
7. MAJOR POTATO PESTS ___________________________________ 39
7.1. Leafminer fly ____________________________________________ 39
7.2. Potato tuber moth ________________________________________ 40
7.3. Aphid___________________________________________________ 41
7.4. Thrips __________________________________________________ 42
7.5. Cutworm ________________________________________________ 43
7.6. White grub ______________________________________________ 44
7.7. Mole cricket _____________________________________________ 45
7.8. Whitefly_________________________________________________ 45
7.9. Spider mite ______________________________________________ 45
7.10. Picture of major potato pests _______________________________ 47
8. MAJOR NATURAL ENEMIES OF POTATO PESTS ______________ 49
8.1. Predators _______________________________________________ 49
8.1.1. Ladybird 49
8.1.2. Ground and rove beetles 49
8.1.3. Hoverfly 49
8.1.4. Spider 50
8.1.5. Praying mantis 50
8.1.6. Earwig 50
8.1.7. Predatory fly 50
8.1.8. Other predators 51
8.2. Parasitoids ______________________________________________ 51
8.2.1. Parasitoids of leafminer fly 51
8.2.2. Parasitoids of other potato pests 51
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TABLE OF CONTENTS
8.3. Pathogens ______________________________________________ 52
8.3.1. Granulosis Virus (GV) 52
8.3.2. Bacillus thuringiensis (Bt) 53
8.3.3. Nematodes 53
8.3.4. Fungal pathogens 53
9. DISEASE ECOLOGY ______________________________________ 55
9.1. Plant diseases and their causes ____________________________ 55
9.2. Disease management _____________________________________ 55
9.2.1. Principles of disease management 55
9.2.2. Biological control 57
9.2.3. Chemical control 57
10. MAJOR POTATO DISEASES________________________________ 59
10.1. Bacterial diseases ________________________________________ 59
10.1.1. Bacterial wilt 59
10.1.2. Blackleg or soft rot 60
10.1.3. Common scab 61
10.2. Fungal diseases (mold) ____________________________________ 62
10.2.1. Late blight 62
10.2.2. Early blight 66
10.2.3. Fusarium wilt 67
10.3. Viral diseases ____________________________________________ 67
10.3.1. Leafroll virus 68
10.3.2. Potato Y virus 68
10.3.3. Mosaic virus 69
10.4. Diseases caused by nematodes _____________________________ 69
10.4.1. Root-knot nematode 69
10.4.2. Golden cyst nematode 70
10.5. Problems caused by environmental factors ___________________ 71
10.5.1. Low temperatures 71
10.5.2. Nutrient deficiencies 71
10.6. Picture of major potato diseases ____________________________ 72
11. WEED ECOLOGY _________________________________________ 75
11.1. Weeds: damaging or beneficial? ____________________________ 75
11.2. Weed types ______________________________________________ 75
11.3. Weed management _______________________________________ 75
12. HARVEST AND POST-HARVEST MANAGEMENT ______________ 77
12.1. Pruning plants before harvesting____________________________ 77
12.2. Harvest time _____________________________________________ 77
12.3. Harvesting methods and estimating yield _____________________ 77
12.4. Treatment of produce _____________________________________ 78
12.5. Marketing and prices ______________________________________ 79
12.6. Potato processing ________________________________________ 79
12.7. Analyses of the potato enterprise ___________________________ 79
REFERENCES_______________________________________________ 81
GLOSSARY _________________________________________________ 82
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TABLE OF CONTENTS
vi
ALL ABOUT POTATOES

1.
INTRODUCTION
1 INTRODUCTION
1.1 Integrated pest management: an overview
Integrated Pest Management (IPM) grew from a history of damage to agricultural
environments resulting from inappropriate cultivation practices. The green revolution,
which aimed at increasing agricultural productivity to meet the growing need for food,
in fact gave rise to new problems. The green revolution only stressed higher
productivity, while ignoring the capacity of the environment to support continued use
and paying no attention to increasing farmers’ incomes.
In Indonesia, the green revolution came into being through the so called mass
guidance and mass intensification programs, which focused on promoting improved
seeds, pesticides and chemical fertilizers to farmers. Pesticides and chemical
fertilizers did initially result in substantially larger harvests, but were utilized unwisely
without any clear understanding of exactly how to use them. Ultimately, farmers
became dependent, unable to farm their fields without using chemical fertilizers and
pesticides.
The program had negative effects and led to fresh problems such as new pests,
problems controlling pests and diseases, environmental pollution, and farmers’
dependence on products from outside. Farming sustainability became threatened, as
it was no longer profitable. These problems lead to the realization that the farming
system had to change. The central problems were those relating to pests, therefore,
pest management had to become an important focus of attention.
In 1986, Integrated Pest Management (IPM) began with rice crops in Indonesia.
Initially, the basic concept of IPM was a pest management approach stressing
balanced agroecosystems and making the best possible use of nature. The hope
was this concept could change farmers’ minds away from "pest eradication" and
towards "pest management". The "management" approach emphasizes a balance
between pests and natural enemies in a managed environment able to support that
balance. You do not eradicate pests, but manage them in such a way that their
numbers do not damage crops. When you eradicate pests, you also exterminate their
natural enemies, as pests and natural enemies are mutually interactive.
The basic principles of IPM are:
• Grow a healthy crop.
• Conduct routine field observations to look at development of pests, diseases,
weeds, plants, natural enemies, and the surrounding environment.
• Preserve natural enemies.
• Farmers as IPM experts in their own fields.
The original concept has now changed. IPM no longer focuses on pests alone, but
has expanded to encompass the whole cultivation system. IPM combines various
approaches and technologies in an effort towards sustainable and healthy farming.
IPM will be more effective when implemented across whole farming blocks with
groups of farmers than in individual fields as to ensure a stable ecological balance at
the ecosystem level. IPM has to be the concern of farmer groups, traders,
consumers, government agencies, non-governmental organizations, and farming
businessmen.
A HANDBOOK TO THE ECOLOGY AND INTEGRATED MANAGEMENT OF POTATO 1

1.
INTRODUCTION
Originally, IPM was developed for rice crops and its concepts were socialized
through Integrated Pest Management Farmer Field Schools (IPM FFS). Rice IPM
FFS were first launched in 1989 in Indonesia through the National IPM Program.
Later, when IPM was developed for vegetables and potatoes, complicated problems
experienced by farmers in intensified potato cultivation led to an IPM approach
different from the one used for rice.
1.2 Potatoes: an overview
The potato (Solanum tuberosum) originates from South America, most likely from the
central Andes in Peru. The potato was domesticated and has been grown by
indigenous farming communities for over 4,000 years. Introduced into Europe in the
sixteenth century, the crop subsequently was distributed throughout the world,
including Asia (Smith, 1995).
The potato is a major staple fulfilling human nutritional requirements. Worldwide, the
potato comes forth in terms of production after wheat, maize, and rice. In many
countries potato serves as their staple food because of its excellent nutritional
content.
According to Indonesian farmers, the advantages of the potato over other crops are:
• Its potential for high productivity.
• Its potential for being extremely profitable and easily marketed.
• Its price is relatively stable.
Its production challenges include:
• It is vulnerable to pests and diseases hence implying a high risk of failure.
• Growing potatoes requires substantial capital.
• It needs intensive care and attention.
The main constraints to potato farming in Indonesia are farmers’ lack of healthy seed,
and attack by late blight, bacterial wilt, viruses, and leafminer fly. Other important
constraints for farmers include potato tuber moth, weeds, unfavorable weather, low
soil fertility, inadequate post harvest management, and marketing.
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ALL ABOUT POTATOES

2.
POTATO PLANT GROWTH AND DEVELOPMENT
2 POTATO PLANT GROWTH AND
DEVELOPMENT
2.1 The potato plant
The potato plant consists of the following parts: leaves, stems, roots and tubers.
Some potato varieties planted in particular environments can produce flowers and
berries. The function of each of these plant parts are as follows:
• Leaves are the part of the plant used for supplying nutrients.
• Stems are for supporting plants, and have vessels and growth cells inside.
• Roots absorb nutrients from within the soil.
• Tubers are receptacles for storing nutrients.
2.2 Potato plant growth
There are no fixed development stages in potatoes as these are influenced by
varieties, shoot size, soil fertility, weather etc. Unlike rice, potato development
stages overlap with each other making it difficult to distinguish between stages. For
example, sometimes during the early growth stage, developing tubers have already
begun to grow from the roots. Nevertheless, a division of potato growth stages can
provide a picture of crop's critical development periods. This knowledge is
extremely important for developing management strategies.
Potatoes planted from seed have the following growth stages:
Sprout development stage
This stage begins with several eyes sprouting when the tuber is in storage,
continues through planting and up until shoots emerge from the surface of the
soil. The time involved for the shoots to emerge from the ground varies
greatly depending on the length of the shoot, moisture in the soil and
other environmental conditions. With a sprout at the ideal length of 1-2
cm, shoots should begin emerging from the ground at around 21-30
days after planting (DAP). During this stage the plant still uses nutrient
reserves stored in the tuber.
Vegetative growth stage
This stage shows rapid growth of leaves, stems, new shoots and
roots. The plant still relies on food reserves stored in the seed tuber,
but has already begun to take small quantities of nutrients from the
soil. With the Granola variety this stage generally occurs between 30-
50 DAP.
Tuber initiation stage
In the Granola variety, although tuber-forming roots begin to form
during the vegetative stage, formation of actual tubers only occurs at
40-55 DAP. This stage takes place over a relatively short period of
about 10-15 days. Tubers formed after 65 DAP will not reach
optimum size when harvested. Plants require nutrients in large
quantities during this stage.
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2.
POTATO PLANT GROWTH AND DEVELOPMENT
Tuber bulking stage
At this stage the plant itself has already stopped growing, and only
the tubers become any larger. In the Granola variety, this stage
occurs at 50-80 DAP.
Tuber maturation stage
Yellowing leaves and drooping stems characterize this
stage. Tuber skins gradually harden and do not pare
away easily. Tubers harden due to their increased starch content. In
Granola variety this stage occurs at 80-95 DAP. The best time to
harvest a plant is at over 100 days old, because tubers will have
reached maximum maturity signified by their hardness and sturdy
skins.
2.3 Potato growth stages and vulnerability to pests and disease
At each growth stage plants are vulnerable to certain pests and diseases (see
figure 1). The critical time for a potato plant is during the vegetative growth and
tuber formation stages. Severe pest and disease infestations during these stages
can reduce yield and can even cause crops to fail. Experience from highland areas
in Indonesia shows leaf wilt infection at 30-45 DAP, along with high levels of rainfall
and humidity, causes plants to die before forming tubers. Appropriate plant
management and pest and disease control during the critical growth stages will
support successful potato cultivation.
Days after planting 20 30 40 50 60 70 80 90 100
ARTHROPOD PESTS
Leafminer fly
Potato tuber moth
Aphid
Thrips
Cutworm
White grub
Mole cricket
Armyworm
Looping caterpillar
Whitefly
Mite
DISEASES
Late blight
Bacterial wilt
Virus
Soft rot
Common scab
Early blight
Dry rot
Nematode
Legend:
Commonly found and harmful
Rarely found and not so harmful
Figure 1: Potato growth stage and vulnerability to pests and diseases
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ALL ABOUT POTATOES

3.
SOIL
3 SOIL
3.1 Soil ecology
What do we imagine when we hear the term soil? Something made up of piles of
dead creatures possibly, or leaf litter, sand or dust. However, soil is much more than
that. Soil can be called a living entity, because within it there are millions of different
living organisms. Some are large and visible; others are so small that we cannot see
them with the bare eye. Examples of larger ones are white grubs, mole crickets,
crickets and earthworms, while smaller ones are fungi, bacteria and nematodes. The
total mass of living organisms, including plant roots in a 20 cm deep area of soil
covering one hectare is around 5,000 – 20,000 kg.
The living organisms in the soil interact with each other, in that some are mutually
beneficial, while others are detrimental to one another. Mole crickets and white grubs
are pests that attack plants, roots and tubers under ground. Some bacteria and fungi
cause plants to become sick; while other bacteria and decomposers break down
plant remnants turning them into fertile humus.
Soil that contains no living organisms will become degraded as leaves cannot
decompose and are left to pile up on the soil surface. They will not decompose and
form the nutrients that plants need.
Soil is a vital resource that must be preserved to support farming sustainability. In
order to maintain life in the soil:
• Organic matter must be kept and added when necessary, as it can increase the
diversity, quantity and roles of beneficial living organisms.
• Contour crops, cover crops and build terraces to prevent soil erosion.
• Soil must not be polluted with pesticides. Pesticides kill off beneficial organisms
and can upset the soil’s ecological balance.
3.1.1 Soil types
Soils are composed of three essential minerals – sand, clay and loam. There are
three classes of soil:
• Clayey soil. Made up mainly of clay and silt, it is difficult to work when dry, is
tough, and does not absorb water easily.
• Sandy soil. Dominated by sand and characterized by its ability to absorb water
and be worked easily. This soil type can lose its organic content easily, so a lot of
organic matter must be added in order to maintain fertility.
• Loamy soil. The most prevalent component is sand, but this is balanced with clay
and silt. Loamy soil usually has the good characteristics of clay and sand; it has a
friable nature, the ability to hold water well and is fertile. This soil is often found in
mountainous regions or on the slopes of volcanoes. Loamy soil is suited to all
crops, and particularly to potatoes.
You can determine soil types by doing a "Sediment test":
• Put soil samples into clear bottles,
• Add water at a ratio of 3 parts water to 1 part soil,
• Shake the bottles until the water and soil are thoroughly mixed together,
• Leave to settle,
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3.
SOIL
• Observe the sediment: the top layer of sediment will be loam, under that will be
clay, with sand at the bottom.
• Compare these three components, and determine each soil type based on the soil
textural triangle (See figure 2).
Figure 2: Soil textural triangle
3.1.2 Soil acidity
The pH of soil indicates the level of acidity and is measured by using a pH meter.
Unfortunately this is quite expensive, so a cheap and easy method for measuring pH
balance is to use litmus paper, which you can buy at any pharmacy. Instructions on
how to use it will be found on litmus paper packaging. The lower the pH level, the
higher the acidity, while the higher the pH level, the lower the acidity. Potato plants
grow well in soil with a pH value of between 5.0 and 6.5. Potatoes planted in soil with
pH levels lower than this will produce poor quality tubers and abnormal growth.
Potatoes planted in high pH soil will have problems with common scab.
Generally, soils in potato producing areas have high acidity or pH levels below 5.0.
The lower pH soil is caused, among other things, by the use of acidic chemical
fertilizers, particularly urea and ammonium sulfate. Adding lime and/or reducing use
of urea and ammonium sulfate fertilizers can increase the pH level of a soil. One kind
of liming material is dolomitic limestone, which is added to soil four weeks before
planting. Quantities have to be adjusted in accordance with requirements and soil
type. The amount of lime required is measured based on the initial soil pH and the
desired pH increase. Estimated amounts of lime required for increasing pH of
different soil types are displayed in Table 1 below. It may take several seasons
before the soil pH is close to neutral. Liming of soils with a pH higher than 6 is not
recommended, since further increase in pH may induce potato common scab.
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3.
SOIL
Table 1: Lime requirements as per soil type and pH value
Initial pH
Lime needed, by soil type (t/ha)
Sandy Loamy Clayey
6.0 1.0 1.7 2.4
5.5 2.2 3.7 4.9
5.0 3.2 4.5 7.3
4.5 3.9 7.3 9.7
4.0 4.9 8.5 11.2
3.1.3 Soil conservation
Erosion is a crucial problem in mountainous potato producing areas. The likelihood of
erosion is very high, due to sloping fields with steep gradients and high rainfall.
Erosion causes the surface layer of soil to be carried away. This layer (20 cm or less)
is fertile and rich in nutrients and therefore essential for healthy potato production.
Land management principles for controlling erosion are as follows:
• Ensuring soil is always covered with vegetation, by planting cover crops at times
when production crops are not being cultivated. Exposed soil is easily affected by
rain, flowing water and sunlight causing it to become degraded and easily carried
away by water.
• Sustained use of organic matter can improve soil structure, as it can act as an
adhesive. Soil with high organic matter content is not easily dispersed, and
therefore not easily carried away by surface water.
• Contour crops on areas with steep gradients. These should not interfere with main
crops, so you should choose plant species that do not grow too tall and use wide
plant spacing. Potato crops are more susceptible to pests and disease in shady
conditions.
• Making bench and live terraces as these can contain the flow of water and reduce
erosion. Live terracing is done by planting terraces with slope
reinforcing/contouring crops.
• Making rows of raised beds running across the gradient.
• Making irrigation systems that reduce the speed of flowing water. Make water
channels slightly sloping so they do not cause flooding in the field. Potatoes
become very vulnerable when inundated with water, as humidity increases and
stimulates fungal and bacterial growth, thus causing disease.
3.2 Soil fertility management
3.2.1 Nutrients in the soil
Soil contains nutrients that support the growth and development of plants. Types and
quantities of nutrients needed depend on the growth stage of a plant.
Plants cannot use all the nutrients found in the soil, because most of them are
bonded to soil particles and are therefore unavailable. Plants can absorb nutrients
when they are dissolved in ground water. Factors influencing the availability of
nutrients in the soil are:
• The content of each nutrient in the soil.
• The availability of water in the soil - Good soil conditions are when sufficient water
is available. The field is neither too dry nor inundated with water.
• Soil type and structure – If soil is too dense it bonds to nutrients, meaning plants
cannot absorb them.
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3.
SOIL
• Rainfall - Rain causes washing off of nutrients and reduces their availability.
• Soil pH - Low pH causes the soil to release certain nutrients making their content
too high and poisonous to plants. High pH causes certain nutrients to be tightly
bonded by the soil, making them unavailable as plant nutrients.
3.2.2 Types and functions of nutrients
Nutrients are grouped into two types:
• Macro nutrients - these are nutrients potato plants require in large quantities.
Macro nutrients are nitrogen, phosphorus, potassium, calcium and magnesium.
• Micro nutrients - these are nutrients required in relatively small quantities. Some
nutrients included in this group are boron, zinc, calcium, iron, etc. Even though
they are only needed in small amounts, they are vital for supporting plant growth.
Many micro nutrients are found in organic fertilizer.
Common functions of macro nutrients are described below:
A. Nitrogen (N)
Function:
• Stimulates plant growth and enlarges leaves and tubers.
• A component of chlorophyll helping plants to absorb sunlight and produce
carbohydrates.
• Increases tuber protein content.
Important points:
• Required in larger quantities than any other elements.
• N-containing compounds are very unstable and hence easily lost from soil through
washing off, evaporation and organic/microbial activity.
• Potato crops need N particularly during the vegetative growth, tuber initiation and
tuber bulking stages.
B. Phosphorus (P)
Function:
• Plays a part in chemical processes in plant growth.
• Encourages root and tuber development.
Important points:
• P is very stable, but bonds tightly to soil particles making it quite insoluble in soil
water and difficult for plants to absorb.
• Very high P content can poison and kill plants.
• Potato plants need P particularly during the vegetative growth and tuber initiation
stages.
C. Potassium (K)
Function:
• Stimulates leaf growth.
• Stimulates tuber growth and enlarges tubers.
• Plays a part in producing proteins.
• Counteracts the effects of excessive application of P.
• Increases resistance to disease.
• Improves tuber quality, reduces sugar content and improves storability.
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3.
SOIL
• Increases vitamin A content.
Important points:
• K is relatively easily soluble in water and hence washed off in the soil.
• Excessive quantity of K can poison plants.
• Potato plants need K during the vegetative growth and tuber initiation stages, and
especially during the tuber maturation stage.
D. Calcium (Ca)
Function:
• Proper cell division and elongation
• Proper cell wall development
• Nitrate uptake and metabolism
• Enzyme activity
• Starch metabolism
Important point:
• Calcium helps reduce soil pH.
• Calcium does not easily leach from soils, but over time moves to deeper layers.
Sub-soils are therefore often richer in Calcium.
E. Magnesium (Mg)
Function:
• Essential for chlorophyll formation; Mg forms the central part of chlorophyll.
• Carrier of phosphorus in the plant .
• As enzyme activator and a constituent of many enzymes.
• Sugar synthesis.
• Starch translocation.
• Plant oil and fat formation.
• Nutrient uptake control.
Important point:
• Potato plants need Magnesium in the early sprout development and vegetative
growth stages in order to produce green tissue.
• Deficiency of Magnesium leads to leaf yellowing with brilliant colors.
• Excess causes calcium deficiency.
3.2.3 Testing soil to determine fertilizer needs
Fertilizer requirements depend on quantities of nutrients already available in the
environment (soil, water and air) and to what extent plants require these nutrients. If
quantities already available are lower than plants’ needs, then fertilizer is applied.
Excessive application can damage plants and waste money, while applying too little
can prevent plants from growing to their optimum size.
It is possible to determine what nutrients are present in the soil by testing soil
samples. These tests can be conducted in laboratories. Simple Soil Test Kits,
available in several Asian countries for ready use in the field, can also provide
farmers and extension workers good indications of available nutrients in soil and
corresponding fertilizer management requirements. If so desired, soil testing should
be done 2-3 weeks before planting potatoes. Soil nutrient content varies greatly from
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field to field and at different times of year, however, testing is not necessary every
season.
3.2.4 Organic fertilizers
A. The role of organic matter
Organic matter consists of the substances originating from plant remnants and
animal remains and contains nutrients beneficial to soil health. The need for organic
matter is unlimited, the more added to the soil, the better the soil will become.
Organic matter functions to:
• Increase soil friability - Organic matter will balance soil forming components
making soil crumble easily. Friable soil is important for supporting tuber growth.
• Increase soil fertility - Organic matter contains and gradually provides many macro
and micro nutrients.
• Increase beneficial organisms in the soil, such as decomposers of plant remnants.
• Positively influence soil temperature and moisture levels.
B. Compost
Compost results from the decomposition of various forms of organic matter. It plays
an essential role in enriching nutrient content in the surface layer of the soil. Finished
compost contains an abundance of nutrients.
The benefits of using compost are:
• Compost contains readily available nutrients for plants. In the composting process
raw organic matter decomposes and becomes ready for plants as nutrients to
absorb.
• Compost contains a balanced composition of both micro and macro nutrients.
• Compost is made from materials that are readily available in the farm
environment, such as plant remnants and/or animal feces.
• Compost facilitates good soil structure. High levels of organic matter in the soil
can improve its capacity to hold water and increases soil friability thus simplifying
tillage.
• Compost increases the diversity and quantity of beneficial living organisms in the
soil and suppresses the development of damaging living organisms.
Disadvantages of using compost:
• Required in large quantities to supply the required amount of nutrients. Optimal
use of organic fertilizer for potato crops is 20 tons/ha.
• Labor intensive, both in its production and application.
• Compost takes a long time to make: 1-4 months.
• Unfinished compost may still contain pests and diseases that are dangerous to the
potato crop.
There are various ways to make compost and different farmers use different
methods. However, the general principles of making compost are as follows:
• Collect raw materials for compost (plant material and/or animal feces). Compost
made from a combination of greenery and dung has a better composition than
compost made from only one of the two. All greenery, including weeds, can be
used as raw material for compost.
• Sort the raw materials. This stage is done to remove pollutants such as plastic, tin
cans etc. that will not decompose, and plants infected with diseases (rotten potato
tubers, diseased potato plants etc.)
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• Removing diseased plant materials is not necessary if composting is done well,
i.e. when sufficiently high temperatures (45-65°C) are reached throughout the
compost heap, and over a sufficiently long time period (approximately 12 weeks).
• Mix all materials evenly and pile them up, while adding water and lime to a height
of 1-2 meters. To allow air to flow through the compost, stick a piece of bamboo
with holes bored in its sides into the middle of the pile.
• To accelerate composting, starters can be added such as animal internal organs,
plant remnant composting bacteria and/or commercially-available starters.
• The compost should be turned and observed at least once a month. The
composting process occurs when the temperature of the pile increases (up to
60°C).
• The pile should be watered if it is rather dry and covered when it rains.
• Take the finished compost. Not all the raw materials in the compost will be
decomposed, particularly plant stems, branches etc. Therefore selection of
unfinished materials is necessary before the compost can be applied to the fields.
Characteristics of finished compost:
• The temperature of finished compost has gone down to the same level as that of
the surrounding environment. This shows that the decomposition process has
taken place because all the raw materials have been thoroughly broken down and
become softer.
• The smell of the compost has changed to a fresh earth smell.
Important considerations when making compost:
• Composting requires oxygen from the air, so covering compost heaps with plastic
for too long is not recommended.
• Composting requires humid air for decomposers to work effectively, however, if it
is too wet, the composting process will cease. So, if a compost heap is set up in
the open air, make sure to cover it when it rains.
C. Cover crops, green manure and mulch
Cover crops are crops planted to cover a field when it is not being used for growing
crops. The aim of planting cover crops is to improve soil fertility, control weeds and
prevent erosion. Cover crops are not harvested but dug into the soil when it is tilled.
They need to decompose first before the nutrients are available for the next crop.
Suitable cover crops are legumes, because they can increase the nitrogen content of
the soil.
Green manure is greenery (non-decomposed plant remnants) applied to the soil. As
with cover crops, green manure needs time to decompose and become beneficial to
plants as a source of nutrients. It is best to apply green manure one month before
planting.
Mulch is a soil cover used when potato crops are cultivated. Types of mulch that can
be used are plastic mulch (black-silver, black, or transparent) and organic mulch
(rice-straw, groundnut foliage, etc.).
The benefits of mulch are:
• A more stable microclimate in the soil by regulating temperature and moisture,
which promotes plant growth.
• Increased availability of nutrients in the soil as a result of higher activity of soil
microorganisms that decompose organic matter at more favorable soil
temperature and moisture.
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• Prevention of erosion and washing of organic and inorganic (chemical) fertilizers.
• Prevention of weed growth thus reducing competition between main crops and
weeds.
• Reduction of production costs because no weeding is required on fields using
mulch, and inorganic fertilizer dose can be reduced.
Its disadvantages are with soil infected by bacterial wilt, as applying mulch increases
temperature and moisture levels accelerating growth of wilt causing bacteria. Also if
plastic is left lying around after several seasons’ use, it becomes a source of
pollution.
D. Manure
Manure has the same function as other organic fertilizers, but is richer in nitrogen,
because of its urine content. Different types of manure have different water and
nutrient composition depending on the type of animal providing the manure and the
food it got (see Table 2).
Table 2: Water and nutrient content of several types of manure
Source of manure
Nutrient content (kg/ton)
Water content
Nitrogen Phosphorus Potassium
(%)
Beef cattle 85 26.2 4.5 13.0
Dairy cattle 85 22.0 2.6 13.7
Poultry (chicken, duck etc.) 62 65.3 13.7 12.8
Pig 85 28.4 6.8 19.9
Sheep 66 50.6 6.7 39.7
Horse 66 32.8 4.3 24.2
Manure can be applied before or after it is decomposed. Direct application of nondecomposed
manure is not recommended for the following reasons:
• It may contain pests and diseases that can negatively affect plant health.
• It is difficult to apply because it smells bad and is too wet.
• Applying fresh manure at planting time can actually temporarily reduce quantities
of available nutrients in the soil, because of decomposers using nutrients for
decomposition processes.
• Fresh manure needs the oxygen in the soil in order to decompose, so direct
application can starve plants of oxygen.
• It contains toxic gases that can kill plants.
• It reduces soil pH.
3.2.5 Chemical fertilizers
Chemical fertilizers are fertilizers that contain one or a few nutrients (see Table 3)
and are mined or produced in factories. The most common nutrients contained in
chemical fertilizers are nitrogen (N), phosphorus (P) and potassium (K). Chemical
fertilizers are generally applied directly to the soil. They contain nutrients in a form
that plants can readily absorb, so they must be applied when plants require them.
Chemical fertilizers are categorized according to their composition into single nutrient
and compound fertilizers. Single nutrient fertilizers are chemical fertilizers that
contain one type of nutrient. For example, KCI contains potassium, Urea contains
nitrogen and SP- 36 contains phosphorus. The benefits of using single nutrient
fertilizers are their cheaper prices and they can be applied to suit plants’
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requirements for a certain nutrient at any given crop growth stage. For example if a
plant only needs N then you only need to apply urea. In certain conditions, single
nutrient fertilizers can be mixed to replace compound fertilizers. To mix them
properly, you need to know the nutrient content of each single nutrient fertilizer.
Table 3: Types of common chemical fertilizer in Indonesia and their nutrient content
Fertilizer type Nutrient content (%)
N P 2 0 5 K 2 0
Urea 46 0 0
KCI 0 0 50-60
SP-36 (super phosphate) 0 36 0
Ammonium sulfate 21 0 0
NPK (compound) 15 15 15
Compound fertilizers contain fixed quantities of more than one nutrient. NPK, for
instance, contains 15% of N, P and K each. The advantages of these fertilizers are
they are easy to apply and easy for plants to absorb. However, compound fertilizers
are more expensive, contain relatively small quantities of nutrients and you cannot
apply the individual nutrients in the required proportion to suit specific needs.
The advantages and disadvantages of organic versus chemical fertilizers are
summarized in Table 4.
Table 4: Advantages and disadvantages of organic versus chemical fertilizers
Advantages
Disadvantages
Organic fertilizer
• Rich in balanced nutrient content
• Increases soil friability and health
• Improves soil water-holding capacity.
• Releases nutrients in stages, suiting
plants’ ability to absorb them
• Contains decomposers that play an
important role in increasing soil fertility.
• Stimulates growth and the work of
beneficial living organisms in the soil
• Farmers can make it themselves from
readily available materials
• Required in large quantities
• Actual nutrient content not known and
highly dependent on raw materials
• Application is more difficult as it is
more labor intensive
Chemical fertilizers
• Contain recognized quantities of
certain nutrients
• Releases nutrients into the soil
quickly making them immediately
available to plants
• Easy to determine dose
• Easy to apply
• Very water soluble and easily lost
through washing off
• Carriers may have negative effects on
soil.
• Relatively expensive
3.2.6 How to apply fertilizer
Successful fertilizer use is determined by application strategy covering fertilizer
types, dosages, times and methods. Application strategy is based on a crop’s
nutrient requirements during different stages of its growth. In IPM there are no fixed
recommended doses for fertilizers since the required dose depends on the specific
conditions in a specific field. Table 5 below provides some guidelines that, however,
should be tested and adapted in each specific field. General principles for the
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application of the various commonly used fertilizers are given in the paragraphs
below.
Table 5: Fertilization strategy for potato
Growth stage Application time Type of fertilizer Dose
Soil preparation
Sprout development
stage (planting)
Vegetative growth and
tuber initiation stages
2-4 weeks before
planting
At planting
30-35 days after
planting
Organic 100%
Phosphorus
75% of total dose
Nitrogen
25% of total dose
Phosphorus
25% of total dose
Nitrogen
75% of total dose
Potassium
100% of total dose
A. Organic fertilizer
• Apply at planting time by mixing it straight into the soil or by placing it to the left
and right of the seeds.
• Organic fertilizer requirements for potato crops are minimally 20 ton/ha. Using
more than this will further improve soil structure and fertility.
B. Nitrogen
• Is particularly needed during the vegetative growth and tuber initiation stages.
• Nitrogen is very soluble and volatile, so is best applied in split application. Avoid
applying it when fields are flooded or there is water flowing on the surface of the
soil. Nitrogen evaporates easily so should be covered over by soil immediately
after application.
• It is best to do two (or three) applications, applying 25% at planting (0 DAP) and
75% at 30-35 DAP, by putting it 10-20 cm deep into the soil.
• To save energy and expense, you can apply nitrogen fertilizer at the same time as
weeding and hilling up.
C. Phosphorus
• Required during the vegetative growth and tuber bulking stages.
• P fertilizer takes time to release its P content into a form readily available for
plants to absorb. It bonds easily to minerals in the soil.
• It is best to apply it at planting time as basal application.
• Soils in mountainous areas generally contain natural P, so they need little P
content fertilizer.
D. Potassium
• Is essential during the tuber bulking stage.
• K fertilizer releases its K content in a form available for plants.
• K fertilizer is applied once at 30-35 DAP.
• K easily dissolves in water and should therefore be covered by soil after
application.
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3.2.7 Potato plant fertilizer requirements
Balanced fertilizer use will produce healthy plants that can resist pests and diseases
and compensate for any damage done. For example: adequate levels of potassium
helps hardening the cell walls, making them less penetrable to fungal growth. Healthy
potato plants can produce additional cells around a leafminer fly egg and hence push
it out of the leaf tissue, after which the egg drops to the ground and dies.
Important things to know when applying fertilizer are:
• Plants’ nutrient requirements in relation to estimated yield.
• Quantities of nutrients in the field available for plants.
It is difficult to recommend a fertilizer use balance for potato crops as requirements
vary greatly for different times, seasons, plant types, growth stages and
environmental and market conditions. Fertilizer balance should be based on
experimentation in each location. Farmers’ experiences are the basis for
experimenting with quantities of fertilizers used.
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4 SEED PREPARATION AND
PRODUCTION
4.1 Seed tubers and True Potato Seed
Farmers generally use seed tubers to plant a new crop. However, there is an
alternative known as True Potato Seed (TPS), which is the botanical seed of the
potato plant. TPS is already in use in several potato producing countries, including
India, Vietnam and Indonesia. TPS is not widely used in Indonesia due to a number
of drawbacks. Table 6 summarizes the pros and cons of tuber seed and TPS. The
remaining text of this chapter deals with seed tubers, generally referred to as ‘seed’.
Table 6: Advantages and disadvantages of potato tuber seed versus True Potato Seed
Advantages
Disadvantages
Tuber seed
• Planting technique is relatively easy
and familiar to farmers.
• Seed tubers generally originate from
local crops and are adapted to
prevailing conditions.
• Plants and tubers produced are the
same as parent plants.
• Crop growth duration is relatively short.
• Seeds planted are already sprouting
so there is a high likelihood they will
grow quickly.
• Production is stable when seeds are
selected properly
• Difficult for farmers to obtain quality
seed. Many of the seeds produced by
farmers are infected with viruses,
nematodes and potato tuber moth
larvae
• Seeds need to be stored for a long
time (3-4 months) before they are
ready for planting
• Seed storage and transportation is
relatively expensive
True Potato Seed
• Small quantity of seed required - 120
g/ha, meaning seed cost is relatively
low
• Can be sown when needed. Seeds
can be stored for long periods of time.
When farmers need them, they can be
immediately germinated. Germination
takes 21 days.
• Free from viruses and nematodes.
High production potential.
• Storage and transportation costs are
relatively low
• Cultivation is complicated and requires
a lot of attention, particularly during
germination. Specific training is
recommended
• Cultivation takes more than 120 days
• Some plants and tubers display
unusual characteristics
4.2 Seed generations
We often hear farmers using the terms G0, G1, G2, G3, etc., for potato seed.
Farmers consider G0 potatoes to be better than G1, G1 better than G2, and so on.
But what does G actually mean?
G stands for generation. G0 means generation 0, which is the original parenting
stock from botanical seed or tissue culture. Explanations for the meanings of G0, G1,
and so on, vary greatly from person to person. Some say that imported potatoes
fresh from their crates are G0, so when they are planted their produce is G1. Others
say that potatoes produced by tissue culture are G0 potatoes. A more important
factor than generation is the necessity for using healthy seed, which to a certain
extent is related to generation.
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Some people think that seed generation influences production characteristics.
However, a seed potato not originating from true potato seed will have the same
characteristics as its parent stock, as no hybridization takes place. In the production
process, however, plants can get infected by viruses, which are passed on to the
next generation in seed tubers, as well.
4.3 Criteria for healthy seed
The seed tubers produced by farmers usually originate either from plants they have
farmed themselves, from other farmers, or from seed producers. General criteria for
healthy seed are:
• Seed must originate from healthy parent stock; and be free from disease,
particularly bacterial wilt and viruses.
• Seed bearing plants should be more than 100 days old at the time of harvest.
• Tubers for seed should not be damaged by pests or improper harvest and postharvest
handling. Damaged tubers are more susceptible to diseases that influence
growth.
• Tuber size is not a criterion for healthy seed, however it is best to use seeds of
uniform size, weighing between 40-60 grams/tuber. Seeds of this size are large
enough to provide the nutrients potato plants need during the early stages of
growth, and not too large a volume of seeds will be required per hectare.
• Tuber skins appear fresh and not wrinkled.
• Uniform sprout size of around 1-2 cm. Uniform sprouts will
produce uniform growth, and make it easier to manage pests
and disease (see the chapter on managing leaf rot). Shorter
sprouts will mean plants take longer to emerge from the
ground and extend the plants’ critical period. Sprouts that are
too long will make transporting and planting more difficult as
they are prone to snap easily.
• Robust sprouts with bluish colored bases.
Seed from producers follow certificated standards. Seed potato certification is very
strict making it difficult for farmers to produce them. Certified seed standards are
given in Table 7.
Table 7: Standards for certified potato seed categories
Certified seed category (%)
A B C
Plants in the field
Purity 99.95 99.90 99.50
Bacterial wilt 0.0 0.1 0.5
Dry wilt 0.5 1.0 2.0
Virus 1.0 2.0 3.0
Weak/non-productive 2.0 3.0 4.0
Tubers
Bacterial rot 0.0 0.5 1.0
Dry rot 0.5 1.0 1.0
Black rot 0.5 1.0 1.0
Late blight 1.0 2.0 2.5
Nematodes 1.0 2.0 3.0
Tuber moth larvae 1.0 2.5 3.0
Mechanical damage 1.0 2.0 3.0
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4.4 Seed selection
4.4.1 Positive and negative selection of parent stock
Selecting plants for seed is the key to getting healthy seed. There are two methods of
selection: positive and negative selection. Both of these are done by marking plants
with stake markers.
Positive selection is selecting and marking potato plants as parent stock. Plants
chosen must display good growth and most importantly should show no signs of
bacterial wilt and/or viruses. Negative selection is selecting plants that will not be
used as parent stock. Plants marked are those infected with bacterial wilt and/or
viruses.
Follow selection with a harvesting strategy as follows:
• Removing plant foliage - Plants are pruned at 80 DAP and all foliage is removed.
This is to prevent pests and diseases from moving into the tubers.
• If you use positive selection, then you should harvest the selected parent stock
before harvesting potatoes for consumption or sale.
• If negative selection is used, pull up the marked plants and four plants to the left
and right of them before harvesting the remaining plants. Only tubers from
unmarked plants are used for seed.
4.4.2 Sorting seed tubers
Seed tubers need to be sorted at harvest time, during storage and before planting.
The objectives of sorting are to:
• Remove sources of pests and disease that can damage that seed potatoes.
• Stop pests and diseases spreading from one seed tuber to the others.
• Get healthy seed.
A. Sorting at harvest time
Sorting at harvest time is usually done in the storage area before seed tubers are
stored. Seed tubers are taken from healthy plants chosen either by positive or
negative selection. When sorting, choose seed tubers with smaller class tuber
measurements (less than 60 g/tuber).
B. Sorting in storage
Sorting is done at least twice at one and two months after storage. Some farmers
sort as many as three or four times. This depends on the condition of the seed tubers
at sorting and the amount of time available. If you find high levels of pest and
disease, then you must sort more frequently.
At one month, sort by removing and destroying tubers infected with pests and
disease. Pests appearing during sorting are usually potato tuber moths. At two
months, sort by removing and destroying tubers infected by pests and disease, and
observe sprouting. Turn over and spread out heaped seed potatoes to stimulate
more uniform sprouting.
C. Sorting before planting
Sorting before planting is done twice; once in the storage area and again in the field
before the seed potatoes are planted. Sort in the storage area by removing those
seeds damaged by pests and disease. You should not plant seed potatoes damaged
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by pests and disease. Another important characteristic to pay attention to when
sorting is the uniform length of the shoots. In the field, seed potatoes that have been
damaged in transport should also be separated out.
4.5 Treatment of seed tubers
Before they are put into storage, seed tubers should be cleaned of any soil sticking to
the tuber, as the soil can contain disease. Clean tubers by washing them, or airing
them, spreading them out in the storage area. Any soil stuck to tubers will fall off by
itself. Tubers should be turned over at least once a day to help them dry more
quickly.
To prevent potato tuber moths from infesting the tubers, many farmers apply
chemical insecticides to seed potatoes in storage. This practice is very hazardous to
the farmers’ health, even more so when the seed potatoes are stored in their homes.
As an alternative in areas with severe infestation, farmers can use the biological
insecticide Granulosis Virus (GV) (see chapter 8.3.1). Seed potatoes in storage can
also be covered over using Lantana camera leaves (lantana flowers).
4.6 Seed storage
4.6.1 Storage conditions
Storage conditions influence sprout quality of seed potatoes. Proper storage will
provide high quality, large, robust and uniform-length sprouts. Storage techniques
vary depending on where storage takes place. Sometimes seed potatoes are stored
in sacks, in baskets or spread out on top of each other. Using sacks or baskets can
save space, but can cause uneven sprouting as tubers on the top sprout more
quickly than those underneath. Furthermore, storing sacks or baskets on top of each
other can damage seed tubers making them more vulnerable to pests and disease.
If spread out in storage, tubers will sprouts uniformly. This requires a larger storage
area, which must always be kept dry as damp or wet floors allow diseases,
particularly tuber rot, to affect seed potatoes.
There are three storage lighting categories:
• Dark storage: when there is no light in a storage area.
o Advantages: reduces pest attack in storage and produces seeds potatoes with
more uniform sprout growth.
o Disadvantages: sprouting takes a long time - up to 3 or 4 months. Sprouts are
white in color showing that sprouting is not so good.
• Light storage: when there is full light in a place. This can be sunlight or electric
light.
o Advantages: sprouts are robust and bluish in color, which is a sign of good
sprouting. Storage time is shorter at about 2-3 months.
o Disadvantage: Lighting increases the temperature in the storage area and
causes seed tubers to sprout prematurely. Uneven lighting causes sprouts to
grow irregularly and abnormally, with small and elongated sprouts. Full electric
lighting will increase storage costs. Furthermore, pests like potato tuber moths
enjoy relatively bright places and more damage occurs in these conditions.
• Dark-light combination storage: is a storage technique used to overcome the
drawbacks of the two methods above. Seed tubers are stored in the dark for two
months, and then exposed to full light for the following month.
o Advantages: uniform and robust sprout growth, sprouting time is quicker, and
potato tuber moth damage is low.
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o Disadvantages: requires more than one storage place and is more labor
intensive.
Good storage conditions imply that:
• Seed potatoes are stored in a purpose-built stand-alone storage area with good
air circulation.
• Average temperature in the storage area is kept to 18°C.
• Light conditions are altered using the dark-light method.
• Racks for spreading out seed tubers are used. Allow enough distance between
the racks so you can turn over the seed tubers.
• Seed tubers are not piled up to a depth of more than 20 cm.
• Seed tubers are observed, sorted and turned over once a month.
4.6.2 Pest and disease management during storage
Pests and diseases that can affect tubers in storage are potato tuber moths, bacterial
rot and mold. These diseases are carried by the tubers themselves or caught from
other affected tubers.
Take the following steps to manage pests and diseases in storage:
• Build a good storage area with good air circulation and adjustable lighting. The
temperature inside should not be hot and the air should not be too humid.
• Clear away potato remnants, sacks or any other waste, as these can be breeding
grounds for potato tuber moths.
• Make routine observations looking for pest and disease infected tubers.
• Manually remove and destroy seed tubers affected by pests and diseases.
• If potato tuber moths are a problem, sprinkle GV onto the affected potato tubers.
4.7 Quality seed production
Tuber seed of high quality is best produced from mini-tubers or plantlets that are
derived from either TPS plants or from tissue cultures. This requires special
procedures and equipment, and is only done by farmers who devote their farming to
seed production. The production of quality seed implies the following process:
A. Determine location
Location is all-important in success in quality seed production, because it requires
more intensive handling. Ideal conditions for a location are:
• Close to a water source to facilitate watering,
• Not too far from home or the village to facilitate supervision,
• Shade free so seedling growth is not disturbed. Seedbed nurseries should ideally
run from east to west.
B. Building a screenhouse
A screen house has walls made from soft screen or gauze to prevent insects and
other potentially harmful organisms from entering. Made big enough to suit farmers’
needs, a screen house is simple and inexpensive to build. The frame can be made
from readily available bamboo. The roofs are made of clear plastic and the walls are
closed using nylon gauze. A screen house should have a door that is easy to open
and close. Racks are made inside the screen house for seedling trays.
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C. Prepare seed bed media
Seed beds in screen houses use a media made of a mixture of soil, sand and
manure in a ratio of 1:1:1. The mixture is sterilized (living organisms are removed) by
steaming it for approximately 7-10 hours. This can be done by using an old oil drum.
A layer of water is put in the drum and a sieve is placed above the water to stop the
soil from getting wet. The soil is placed on top of the sieve and bamboo sticks with
holes down its sides are stuck into the middle of the soil mixture to regulate the
temperature. After it has been steamed, the media is spread over the seedbed trays
and allowed to cool.
D. Planting materials and method
Tools needed in this process are a penknife and buckets. Materials necessary are
clean water (mineral drinking water can be used), 95% alcohol, root growth
stimulating chemicals (available in farming supplies shops), tray with media and seed
materials. All tools must be sterilized before use by wiping them with the 95%
alcohol. Seed materials that can be used are mini tubers and plantlets produced from
tissue culture.
How to plant:
• Mini tubers - Plant mini tubers with a spacing of 20 cm x 20 cm at a depth of 5 - 10
cm into the media.
• Tissue culture plantlets - Pull up tissue culture plantlets and clean their roots. You
must do this carefully to prevent roots and stems from breaking. Then plant them
with a spacing of 10 cm x 10 cm.
E. Plant care
Plants are tended while they are growing by removing those plant parts damaged by
pests and disease, as well as loosening media, applying fertilizer and watering. Soil
is loosened and hilled up at 14 DAP. Fertilizer is applied by spraying a solution of
compound fertilizer made by dissolving 5 grams of compound fertilizer in 1 liter of
water.
F. Taking cuttings for propagation
When seed material is growing well, take stem cuttings for propagation at about 8-15
DAP. These stem cuttings, taken from parent stock plants, should be about 3-4 cm
long (1-2 shoots), be dipped in a solution of a root growth stimulating chemical and
planted in different trays with plant spacing of 20 cm x 20 cm. Cuttings should be
taken in the afternoon taking care to use a sterile knife. After planting, shade parent
stock plants and stem cuttings with banana leaves. You may take cuttings five times
from each plant.
G. Harvesting
Harvesting takes place at 75 DAP, or when the plants start to die. Do this by
dismantling the soil around the plants. One plant typically produces 2-4 tubers each
weighting 10-20 grams. Select tubers based on their size and then store them. The
tubers can be used for seed to plant in the fields or propagated in a screen house to
produce the next generation of seed tubers.
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CULTIVATION PRACTICES
5 CULTIVATION PRACTICES
5.1 Choice of location
What are the best conditions for potatoes to grow? Potatoes can grow well in areas
with:
• An elevation of more than 800 meters above sea level. Under Indonesian upland
conditions, the best elevation is over 1,300 meters above sea level.
• Daily temperatures ranging between 10-22°C, with an average of 15°C.
• Around 12 hours of daylight a day.
• Adequate water supply. This could be high rainfall of around 1,500-5,000 mm, with
a balanced pattern of rainfall between the dry and rainy seasons. In areas with
relatively low rainfall, irrigation management is a crucial factor. The best potatoes
are grown in dry irrigated land.
• Friable sandy soil that contains organic matter so it is highly fertile and drains well.
• Soil free from bacterial wilt, nematodes and viruses, particularly when cultivating
seed potatoes.
5.2 Potato varieties
In their place of origin (South America), there are many potato varieties, some of
which are indigenous varieties and others of which are hybrids. Thousands of
varieties with their manifold strengths and weaknesses are cultivated in South
American countries.
Farmers in Indonesia plant very few varieties. The most commonly cultivated
varieties in Indonesia are Granola, Atlantic, and Columbus. Atlantic and Columbus
have almost the same characteristics, but both of these differ from Granola, which is
the preferred and most easily marketed potato variety for Indonesian farmers as it is
familiar and easily marketed. Table 8 shows the differences in the characteristics of
potato varieties commonly grown in Indonesia.
5.3 Field preparation
5.3.1 Tilling the soil
Preparing fields for potatoes requires heavy tillage turning the soil over. You can use
hoes, tractors or ploughs in tilling to a depth of around 20 -50 cm. Hoes are usually
used when tilling the soil to a depth of 50 cm. This is done in two stages: the first is to
a depth of 20 cm, and then the second is digging and turning the lower layer of soil
over for a further 30 cm.
When tilling the field, remove unwanted weeds, especially grasses. Collect the
weeds and burn them after they are dry. Another method is to bury them more than
50 cm down so they cannot grow again. Leave tilled soil for one week in order to
neutralize soil temperature before planting any potatoes.
The benefits of tilling by turning over soil are:
• It allows other parts of the soil to be planted thus maintaining soil fertility.
• It improves the condition of the soil.
• It controls weeds.
• It exposes pests and diseases present in the soil to sunlight and causes them to
die.
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Table 8: Differences in potato varieties commonly grown in Indonesia
Criteria Granola Atlantic-Columbus
Growth
characteristics
• Plant heights average 50-70 cm.
• Stems are small and one clump
consists of 3-5 stems.
• Roots reach a maximum length of
50 cm.
• Only one tuber per root.
• Plant heights average 80-110 cm,
with large strong stems.
• One clump consists of 2-3 stems.
• Roots reach a maximum length of
90 cm.
Age • 90-110 days • Can reach 150 days
Seed
availability
Farmers’ views
on cultivation
Vulnerability to
disease
• Easy. Many farmers can produce
their own seeds or buy them from
seed companies.
• Relatively easy
• Relatively susceptible to leaf rot
and bacterial wilt, but quite
resistant to viruses.
• Difficult. Farmers have trouble
producing their own seeds
because harvested tubers are
large in size.
• Farmers depend on relatively
expensive seeds from seed
companies.
• Relatively difficult
• Long growth duration can affect
normal cropping pattern.
• Relatively susceptible to bacterial
wilt, but quite resistant to leaf rot.
Productivity • Low, averaging 15-18 tons/ha • High, averaging 20-22 tons/ha
Tuber shape • Oval – egg shaped • Oval – long
Sugar content • Relatively high – will burn quickly
when fried and not dry completely.
• Relatively low – suitable for
processing
Uses • Vegetable potato • Processing potato
Marketing • Easy to market, accepted in the
local fresh market (in Indonesia)
• Not so widely accepted in the
local fresh market. Usually sold to
potato processing factories.
Nevertheless, tilling the soil can:
• Change the composition and balance of living organisms in the soil and reduce
soil fertility.
• Increase erosion. Newly tilled soil is very crumbly and easily carried away by
water.
• Accelerate decomposition of organic matter.
To avoid these negative impacts, you need to add organic fertilizer immediately after
tillage and till lightly.
5.3.2 Seedbed preparation
Make raised seedbeds to suit the direction and gradient of the field. They should be
made to run across the slope. If fields are too steep, you will have to level them and
build terraces to prevent erosion.
The width of and distance between raised seedbeds should be made appropriate to
plant spacing. Raised seedbeds are generally made when planting in the rainy
season so furrows are deeper, thus allowing water to flow more easily. Raised
seedbeds should be around 10-20 cm high. You do not need to make raised
seedbeds before planting in the dry season, as they will form when you cover seeds
with soil, weed and hill up.
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5.4 Planting
5.4.1 Planting time
A good time to plant potatoes is at the end of the dry season or the end of the rainy
season. It is best to determine when to plant by considering the critical period for
plants and how that will relate to environmental conditions. The critical period for
potato plants is during the vegetative growth stage. At this stage they should not get
too much rain or wind, or be too dry. Soil should be sufficiently moist when planting,
as moist soil can accelerate plant growth.
5.4.2 Planting method
When planting without mulch, place seeds at the planting points with their sprouts
facing upwards. Apply organic fertilizer to their left and right. Potato farmers generally
apply chemical fertilizer on top of the manure. This is not recommended as it is
untimely, unless the fertilizer contains phosphorus. Cover the seeds and manure with
soil to a thickness of 10-15 cm.
When planting with mulch, make raised seedbeds 40-60 cm high and 60-80 cm wide,
with a distance of 30 cm between the seedbeds. Make the seedbeds after tilling the
soil, and then cover them using black-silver plastic mulch with the silver side facing
upwards. Leave the raised seedbeds for one week, then make planting holes to suit
the desired plant spacing.
For monoculture planting, plant two rows of potatoes in one seedbed, but if you are
intercropping, plant only one row of potatoes in the middle, and plant the other crops
on the edges of the seedbeds. To do this, place seeds and manure into the planting
holes.
Plant spacing varies depending on region and variety. Granola potatoes are normally
planted with a spacing of 30 cm x 70 cm, or 25 cm x 75 cm.
5.4.3 Intercropping
You can intercrop potatoes with other plants such as kidney beans or spring onions.
These can be planted on the edges of the raised seedbeds.
How to plant:
• Plant two rows of kidney beans per seedbed between the rows of potatoes.
• Plant spring onions alternately to the sides of the potato plants.
Advantages of intercropping are:
• It provides another source of income for farmers.
• The other crop can trap or deter insect pests and reduce spread of disease.
• Intercropped plants can attract natural enemies. For instance, parasitoids prefer to
attack leafminer fly larvae on kidney beans planted among potato plants.
• Intercropping with pulses can improve soil fertility, as pulses can harness nitrogen
from the air.
Disadvantages are:
• Intercropping can increase plant density making the environment damper and
stimulating the development of diseases.
• The main and secondary crops compete for space and nutrients.
• The secondary plants can be a source of pests and diseases.
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5.5 Hilling up and weeding
When you use mulch, hilling up is not necessary and weeding only involves pulling
up those weeds present in planting holes or furrows between seed beds. When you
do not use mulch, you should weed and hill up at the same time as applying fertilizer.
Do this at least twice in a planting season; at 30 DAP and 50 DAP.
Weed by pulling up weeds directly or by scraping them out of the soil with a hoe,
collecting them and burying or composting them. If there are not so many weeds and
those present are not grasses, dig them out and pile them up around the plants.
Hilling up is done initially by loosening the soil around the potato plants, and piling it
up around the plants. Seedbed height after the first hilling up should be around 30
cm. For the second hilling up, remove soil from the furrows and pile it up around the
plants. You should do this more carefully to avoid damaging the plant roots. Seedbed
height after the second hilling up should be about 60 cm.
Seedbeds for planting in the rainy season should be higher than those used in the
dry season. This is to reduce soil moisture, which can stimulate development of plant
diseases.
Advantages of weeding and hilling up:
• Covers fertilizer and prevents fertilizer loss resulting from evaporation or washing
off.
• Gets rid of weeds thus preventing competition between potato plants and weeds.
• Loosens the soil helping potato plants to better develop roots.
• Makes water flow more easily down the furrows and prevents flooding in the rainy
season.
• Improves environmental condition of the plants and the soil.
• Covers potato tubers forming close to the surface of the soil, hence reducing the
risk of damage from potato tuber moths.
Disadvantages of weeding and hilling up:
• Can damage potato plant root system.
• Can cause lesions on the roots and tubers, thus increasing the risk of disease.
5.6 Water management
5.6.1 Irrigation systems
Irrigation systems are systems that allow water to enter and leave the field. They
should be planned and constructed before planting begins.
Good irrigation systems:
• Prevent the field from flooding.
• Prevent the entry and spread of water-borne diseases.
• Make it easy for water to enter the field when plants need it, especially in the dry
season.
Potato fields should have a minimum of three lengthwise and three transverse water
channels. For each direction this implies two channels at the edges and at least one
in the middle. These channels should be deeper than the furrows between the raised
seedbeds.
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5.6.2 Watering
Watering potato plants is very important in the dry season. Sloping fields in potato
planting regions make water management a crucial factor in the success of potato
crops. You can irrigate plants in two ways; by using water channels or by watering
using hoses, buckets, etc. Table 9 below shows the advantages and disadvantages
of the two irrigation methods.
Table 9: Advantages and disadvantages of irrigation methods in potato production
Using irrigation channels
Using hoses, buckets, etc.
Advantages
Disadvantages
• Makes the fields wetter
• More even distribution of water across
the field
• Less expensive
• Difficult to do if the water source is far
away and/or lower than the field
• Water flowing in or between fields can
spread water-borne diseases
• Requires a complicated system of
irrigation channels
• Can be done even when the water
source is far from the field
• Prevents water-borne diseases being
carried into the field
• Does not require a complicated system
of irrigation channels
• Watered areas not very wet and
watering is uneven across the field.
• Require more expensive equipment
• Is labor intensive
5.6.3 Water management and water-borne diseases
Water can lead to an increase in diseases in the following ways:
• Increases in moisture levels around plants, caused by flooding for example, can
lead to rises in leaf blight, stem-end rot and bacterial wilt.
• Water can carry diseases from one plant to another. Water-borne diseases
include bacterial wilt and tuber dry rot.
Proper water management in potato fields is essential in preventing the above from
occurring. Key points are:
• Water should be able to exit the field easily when it rains.
• If bacterial wilt is discovered, it is best to water using hoses or buckets to prevent
it from spreading in water flowing on the surface of the soil.
5.7 Crop rotation
Reasons for rotating crops are:
• Avoiding increased levels of pest and disease damage. Potatoes cannot be
planted two to three times in a row. Increased populations of pests and diseases
from one generation to the next make it difficult to achieve satisfactory harvests
with the next crop. This is particularly a concern for Golden Cyst Nematode.
Bacterial wilt will increase in prevalence in the second and third consecutive
crops, leading to a substantial reduction in yield. Even though bacterial wilt
survives for about two years in the soil, rotation with other plants, particularly corn,
cabbage and sweet potato, can reduce levels of infection in the next potato crop.
• Exploiting the most appropriate time for planting potatoes. The success of a potato
crop is influenced by the weather. High rainfall and drought can both cause potato
crop failure. During certain months of the year, farmers should substitute their
potato crops with other safer plants.
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• Maintaining and improving soil fertility. Continual planting of potatoes can reduce
quantities of nutrients in the soil. Potato plants need large quantities of nutrients,
so rotation with crops such as pulses and sweet potato can help maintain and
increase soil fertility.
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INSECT ECOLOGY
6 INSECT ECOLOGY
6.1 Introduction
Ecology is the study of the relationships between living creatures and their
environments. Like humans, insects’ lives are influenced by environmental factors
such as the availability and quality of food, natural enemies and weather conditions.
When they have an abundance of high quality food and supportive weather, and
there are no natural enemies getting in their way, insect pests will increase in
number.
An understanding of the relationships between insects and the factors supporting
their existence is important in order to develop techniques for their management.
This understanding will develop by conducting observations and agroecosystems
analysis. These activities are an essential part of IPM FFS.
In an agroecosystems analysis, farmers look not so much at individual insects, but at
their relative numbers and the roles they play. This is because individual insects
cannot cause economically important damage. Every living creature has its enemies.
Nature maintains a balance between the numbers of prey and predators, insect pests
and their natural enemies. Changes in one of these components will upset this
balance. Insecticides upset the balance between pests and natural enemies, since
natural enemies are generally more susceptible than pest insects and hence may
lead to increased pest numbers and more damage to crops. Farmers must develop
an understanding of the balance between insect pests and their natural enemies in
order to develop strategies for managing insect pests. These strategies should focus
on keeping pest populations at numbers that do not cause yield loss, but support the
development of their natural enemies.
The environment influences the presence of insect pests. Pests prefer the dry
weather of the dry season. Of course we cannot control the weather. We can,
however, gain an understanding of the relationship between the weather and insect
pest life cycles in order to determine planting times and management practices.
Understanding agroecological processes will encourage development of
management patterns that are healthier for farmers, the environment and harvest
produce.
6.2 Insect anatomy
The main body of an adult insect is made up of
three parts: the head, the thorax and the
abdomen. Insect mouthparts vary. For instance, a
grasshopper has mouth parts that bite and chew,
butterfly mouth parts probe and suck, whereas
flies lick. On the thorax are three pairs of jointed
legs and also one or two pairs of wings. Some
insects move around actively while others just
stay on one plant. For example, leafminer flies are
very active and therefore difficult to observe, while
aphids tend to stay on one plant. Adult insects
have hard exoskeletons making it difficult for
contact insecticide to enter their bodies.
Antenna
Head
Thorax
Abdomen
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6.3 Insect life cycle
In their lifetimes insects change their skin and form. Generally, insect life cycles are
divided into three stages, namely egg, larva and adult. Insects change their skin
during each of these stages. During the larval stage, insects change their skin more
than once. When they do, they are vulnerable as they are still weak and their skins
are soft.
The adult stages of many insects, such as butterflies, beetles and mosquitoes, are
very different and feed on completely different things than their larval stages. For
example, certain caterpillars eat plant leaves and stems, while the adult butterflies
feed on nectar.
Grasshoppers, crickets and locusts are almost the same in their young and adult
stages. You can differentiate between these stages by looking for the presence or
absence of wings; adult insects are the ones with wings. These insects eat the same
food in their young and adult stages, and are plant pests. Insect pests are easier to
control before they reach their adult stage because their skins have not hardened
yet, and they do not move around so actively. Exceptions are insect pests that
remain inside plants during their pre-adult stage (e.g., leafminer fly larvae). These are
difficult to control with most insecticides, as those applied do not reach their target.
It is very important to understand the life cycle of insect pests. Generally, farmers are
familiar with the stage of insect pests that affects their plants or tubers, but are
unaware that other seemingly harmless creatures are actually the same species at a
different stage in their life cycle. For example, farmers recognize the caterpillars that
bore into their potato tubers, but consider the moths flying about in their storage
areas to be a different and harmless species.
An understanding of WHAT turns into WHAT, WHERE, WHEN and HOW, provides
information about insects’ strengths and weaknesses at each growth stage, and is
the basis for developing insect pest management strategies.
6.4 Insect pests
Insect pests can damage plants in a number of ways:
• Eating leaves and stems making holes in the plant and breaking off stems. Insects
with biting and chewing mouthparts cause this kind of damage. Examples are
armyworms, cutworms, grasshoppers, and crickets.
• Cutting or boring. Signs are often found on potato leaves and tubers. Larvae bore
into and remain inside leaves hollowing them out and leaving only the dry outer
layer. Tubers become full of holes. Examples are larvae of the leafminer fly and
potato tuber moth.
• Puncturing and sucking. Aphids and thrips are insects with these mouthparts.
Usually they affect young and soft plant parts causing leaves to roll, wilt and dry
out.
• Spreading viruses. Insects can carry viruses from one plant to another. When they
stick their mouthparts into an infected plant, the virus sticks to or enters the insect
and spreads when the carrier moves on to the next plant.
Insects can cause direct and indirect damage:
• Direct damage is caused when a pest attacks a part of a plant that will be
harvested such as the potato tuber.
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• Indirect damage is caused when a pest either attacks parts of a plant that will not
be harvested or spreads disease. For example pests that attack potato leaves,
roots or stems and pests that spread viruses.
Direct damage generally causes greater financial losses than indirect damage. With
indirect attacks, plants have compensation strategies. When leafminer flies infest a
crop during the tuber initiation stage and 20-30% of the foliage is infested, yield will
not be affected because undamaged leaves can still produce enough to bulk the
potatoes.
You can do leaf cutting tests to observe how different levels of pest damage on
leaves can affect tuber yield. The steps for testing loss of produce are as follows:
• Plant potatoes in 12 buckets.
• When they are 35-40 days old, cut off leaves as follows; 0% (no leaves removed)
in 3 buckets, 25% in 3 buckets, 50% in 3 buckets and 75% in the remaining 3
buckets.
• Tend each plant until ready for harvest.
• Harvest each plant, weigh and classify the tubers.
• Make comparisons to see how removing different percentages of foliage affects
plant yield.
When we make observations in the field, we will come across many kinds of living
creatures, insects and non-insects. But do all of these creatures damage potato
plants? Farmers always worry when they find insects on their potato plants and try to
eradicate them with insecticide.
Evidently, not all insects are farmers’ enemies. In fact, only a few of the insect
species in the field will damage crops, while most of them actually help farmers. The
functions of some of the others have yet to be discovered, as they seem to be neither
damaging nor beneficial.
Some insect species eat plants in quantities too small to cause any economic loss.
Spraying these insects with insecticides will not increase harvest produce, but will
increase costs, hence making production more expensive.
Many insects are farmers’ friends because they prey on other damaging insects.
Generally, these species are extremely sensitive to insecticides. Insecticides actually
kill more beneficial than damaging insects.
When you find an insect, ask yourself about its role and function in the agroecosystem:
is it a pest, a natural enemy or playing no part and just passing through?
To answer this question you can set up an ‘insect zoo’, or enclosure, to observe
feeding habits of insects. The steps in this are as follows:
• Isolate several potato plants in the field or in pots. Keep each plant isolated from
other plants.
• Make sure these plants do not get any pesticide on them.
• Place several specimens of one insect species onto each isolated plant.
• Observe insect behavior every day.
• If an insect species does not eat any plant parts within 3 days, put other insect
species inside.
• Observe what happens and keep records.
• Draw conclusions based on observation outcomes.
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6.5 Beneficial insects
Insects that prey on insect pests, or diseases that infect insect pests, are called
"farmers’ friends" or "natural enemies". They help farmers to control the number of
insect pests and prevent damage to crops. Natural enemies can effectively control
many insect pests. Predators, parasitoids, pathogens (diseases) and nematodes are
all classified as natural enemies. The characteristics of natural enemies depend on
their class, as is described below.
Predators:
• Predators stalk and catch moving prey.
• Predators eat many preys of different species in their lifetimes.
• In some insect species, both larval and adult stages of insects can be predators.
In other species, though, only the larval or the adult stage is predatory.
• Predators commonly found on potato crops are spiders, ladybirds, earwigs, hunter
flies, hoverflies, praying mantises and dragonflies.
Parasitoids:
• Parasitoids found on potato crops are specific types of wasps and flies.
• Parasitoids attack their prey when it is vulnerable, usually in their egg or larval
stages, by laying an egg inside or on the top of their victim. The egg will hatch and
the newly emerged larva of the parasitoid slowly consumes its victim.
• Parasitoids only parasitize one insect in their lifetime.
• Parasitoids have very specific relationships with their host.
• Parasitoids are usually much smaller than their host.
Pathogens:
• Pathogens are similar to diseases in humans, such as flu, typhus, tuberculosis
etc. They are extremely small and invisible to the naked eye.
• Pathogens require humidity and certain temperatures in order to infect insects.
• Pathogens are immobile, and wait until they come into contact with their host
before they can cause disease.
• Pathogens can only infect certain species of insects during certain stages of their
development. For example, the pathogen GV on potato tuber moth larvae.
• Fungi, bacteria and viruses are included in this category.
Nematodes:
• Nematodes are tiny worms. Certain species of nematodes can be pests, while
others can act as natural enemies.
To be effective, a natural enemy must:
• Have capacity to develop many eggs and young in order to remain in balance with
the number of insect pests.
• Be highly capable of attacking their prey.
• Be host specific.
• Be adaptable to changing environments.
• Proliferate at the same times and rate as their prey.
Strategies for increasing the effectiveness of natural enemies are:
• Observing natural enemy species in the field - This is essential as the basis for
determining further measures.
• Manipulating the environment - Done when the natural enemies found in the field
are not playing an effective role (despite the presence of natural enemies, insect
pests are still prevalent and causing damage to the crop).
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• Releasing new natural enemies into the field - Done when no effective hostregulating
natural enemies are found, or when they are present only in very small
numbers.
• Making natural enemy release cages – You can do this to increase the number of
leafminer fly natural enemies. Cages measure 1 x 1 x 1m, and are closed on all
sides with gauze. The gauze must have holes large enough for the parasitoids to
escape, but small enough to keep leafminer flies trapped inside. Collect potato
and green bean leaves or weeds showing signs of leafminer fly damage. Put them
inside the cage, the place the cage in the middle of the field making sure to keep it
sheltered from the rain. Parasitoids will escape and survive, while leafminer flies
will be trapped and perish inside the cage.
Ways of manipulating the environment to increase the role of natural enemies are as
follows:
• Accept a low level of insect pests in the field - Insect pests are a food source for
natural enemies. If there are no pests, there will be no natural enemies.
• Not using insecticides - Natural enemies are more sensitive to insecticides. Tests
have shown that natural enemies are more numerous in quantity and species
diversity in unsprayed fields than they are in fields sprayed with insecticides. The
overall result is smaller pest populations in fields that have not been sprayed.
• Planting nectar-producing plants - Adult insects that act as natural enemies
(particularly parasitoids) feed on nectar. Therefore, planting flowers on the edges
of fields will provide food for these parasitoid species and induce longevity.
• Using compost - Predatory flies need compost as a habitat for its maggots.
• If you are forced to use insecticide, do spot applications to affected plants only,
and select insecticides with low toxicity.
6.6 Pest management
6.6.1 Biological control
Natural enemies have been discussed in the section above on farmer-friendly
insects. Biological control will develop better if supported with another strategy, i.e.
using natural pesticides, which originate from plants and are less likely to disturb or
kill natural enemies. Plant materials that can be used as insecticides are the
following:
Neem:
Neem (Azadirachta indica) is a tree that is toxic and repellent to numerous pests,
particularly insect larvae, aphids and thrips. All parts of this plant are toxic, but
toxicity is highest in the seeds.
How to use it: Pulverize plant parts until they are soft, and dilute them with clean
water. Spray the mixture onto plants. To help it stick to the leaves you can add
detergent. Because the toxicity does not last long in direct sunlight, it is best to spray
in the late afternoon. If the mixture is too concentrated, it will poison plants leaving
them looking as if they have been burnt.
Tuba:
The tuba plant (Derris elliptica) is commonly found in tropical forests. All parts of the
plant are toxic, but the roots have the highest toxicity. This plant can be used to
control leaf-eating insects such as caterpillars, grasshoppers, aphids, thrips, etc.
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How to use it: Squeeze plant roots in clean water and leave them to soak overnight.
The water can then be sprayed directly onto the plants. As with neem, you should
spray in the late afternoon, and make sure the mixture is not too concentrated.
The benefits of natural pesticides are:
• They are often cheap and easy for farmers to make.
• They are generally not toxic to humans or livestock.
• They do not pollute the environment, because their residues are easily broken
down.
• They rarely lead to insect immunity.
Drawbacks are:
• Materials are not always readily available to farmers.
• They must be applied appropriately and repeatedly.
• Some natural pesticides also poison natural enemies.
• It is difficult to determine the correct doses to apply.
• Bits of plants often block sprayer nozzles.
6.6.2 Mechanical control
Mechanical control strategies include using traps and trap crops, and manually
removing insect pests.
Effective trap crops for leafminer flies are all kinds of beans, as the flies prefer these
plants to potatoes to lay eggs on. Trap crops contribute to increasing the role of
parasitoids, and can be used as follows:
• Plant beans at the same time as potatoes on the edges of potato beds.
• One week after emergence conduct observations of these plants. Collect leaves
affected by leafminer flies and put them in the parasitoid release cage. Continue to
do observations every other day.
Yellow sticky traps are only appropriate for leafminer flies, as they are attracted to the
color yellow. Initially yellow traps were only used for observing the presence and
quantity of these insect pests, but recently many farmers have been using them as a
means for reducing leafminer fly populations.
Anything yellow such as yellow plastic, yellow painted boards, oil bottles etc. can be
used for making traps. Smear them with something sticky such as glue, starch
solution or old engine oil, then put them in the field about 10-20 cm above the tops of
the plants. You can use bamboo stakes for supporting the yellow boards. Normally
about 80 traps will be used for 1 ha. Position flat traps in line with the path of the sun
(west-east). Traps that gleam in sunlight will be more effective.
Many farmers have changed their insecticide use patterns as a result of the success
of yellow traps. When farmers find lots of leafminer flies on their traps, they feel they
are controlling them successfully and no longer spray insecticide. This supports the
development of natural enemies, increasing their numbers, diversity and impact.
Finally, natural enemies can control leafminer flies by themselves.
Drawbacks of yellow traps are:
• They only trap adult insects, while the actual pest is the larva. Trapped insects
may have already laid their eggs on leaves. Hence, the effects of such traps on
population regulation are limited.
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• Some natural enemies in the parasitoid and predator groups are caught, as they
are also attracted to yellow.
To lessen these drawbacks, do not install yellow traps continuously. Install and
remove every other week. Traps should be removed when natural enemy
populations are increasing.
Insect pests can be removed manually when their populations are not too high. For
this to be effective, it must be done in an organized, thorough and timely manner.
Any pests collected should be destroyed. The drawbacks of this method are that it is
time consuming and labor intensive, and difficult to do with pest species that actively
move around.
6.6.3 Chemical control
A. Introduction
PESTICIDES ARE NOT MEDICINES, BUT POISONS THAT CAN KILL ANY KIND
OF LIVING ORGANISM. Pesticides are generally killers, and are used extremely
inappropriately when applied once a day or every other day. In the rainy season,
some farmers even spray their crops twice a day. Farmers often apply a mix of
several types of pesticide. Frequencies of an average of 15 times per cropping
season have been recorded in certain potato-growing areas in Indonesia.
The main reasons farmers say they use pesticides are that they are easy to use, and
that the results are immediately apparent as many insects are visibly killed instantly.
The improper use of pesticides, however, makes potato production costs very high.
In Indonesia, about 27% of the total costs for production inputs are spent buying
pesticides. When farmers see insects or symptoms of pests or disease, they
immediately assume they should spray their crop with pesticide. In the end, the
pesticides cause more problems than they resolve, as resistance to pesticides
develop and natural enemies are killed.
B. Pesticide types
Chemical pesticides can be categorized in various ways as described below.
Based on their intended targets:
• Insecticides are pesticides intended to kill insects.
• Herbicides are pesticides used to kill off weed growth. Generally, they kill weeds
by destroying plant tissue or accelerating growth.
• Fungicides are pesticides aimed at fungi. Many contain sulfur or copper.
• Rodenticides are used to kill rodents (rats and mice). Several of them are
extremely toxic to other mammals.
• Nematicides are pesticides used to kill nematodes (tiny worms).
• Acaricides are pesticides used for killing mites.
Based on their formulations:
• Emulsifiable Concentrates (EC): Emulsifiable concentrates are thick solutions of
active ingredients in oil that contain detergent-like emulsifiers that allows the thick
solution of active ingredients to be diluted in water to form a solution for spraying
in the field. The important components of EC formulations are the active
ingredients, organic solvents and emulsifiers. Mineral oil solvents are used.
• Water-Soluble Concentrates (WSC) / Soluble Concentrates (SC): These
pesticides dissolve completely in water. Their active ingredients might dissolve in
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water or may already be dissolved in an organic solvent (alcohol for example)
making them water-soluble. The consistency and color of these pesticides are
similar to EC, but become clear after being diluted with water. The important
components in these formulations are active ingredients and organic solvents.
Solvents used are types of alcohol.
• Wettable powder (WP): WP contains active ingredients, a wetting agent and other
materials such as adhesives. The wetting agent allows an even mixture of powder
and water when it is diluted for spraying. Without the wetting agent, the active
ingredients would not mix with water, but float on the surface. Carriers are
generally in the form of mineral powder such as talc or clay. This talc or clay
settles at the bottom of the tank and needs continuous shaking to maintain
suspension.
• Flowable (F): In these formulations, active ingredients are mixed with a carrier (a
mineral powder) and a small amount of water producing a formulation fine but wet
granules. This "wet mixture" is easy to mix evenly with water and can be sprayed
using the same type of sprayers as used for WP formulations. This formulation
requires continuous stirring.
• Soluble Powder (SP): Active ingredients in SP formulations are either in a powder
form that dissolves in water or formed into pellets containing small amounts of
wetting agent to increase water solubility. Different from WP and F formulations,
SP formulations do not require continuous stirring when spraying as the mixture
remains in continual suspension.
• Granules (G): The components of this formulation are an active ingredient, carrier
and adhesive. This mix of materials is made into small granules. Active
ingredients make up around 2-25%. Carriers are clay and mineral substances.
Based on their mode of action:
• Contact pesticides: There are pesticides that kill their intended targets by coming
into contact with them. These pesticides remain on plants just after application,
but are generally only effective for short periods of time and are easily affected by
weather factors, particularly temperature and sunlight. They must be applied
directly to the plant parts where pests and diseases are often found.
• Systemic pesticides: These are pesticides that can enter and spread through all
parts of a plant and affect the pest or disease after it consumes plant parts.
Systemic insecticides generally poison stomachs or nerves, and are effective for
controlling pests that suck, eat plant tissue or bore. Spraying needs not
necessarily be on the affected parts of plants as these pesticides spread to all
parts including the roots. Toxicity of these pesticides is generally long-lasting.
These should not be used before harvesting as they can pollute crop produce and
pose toxicity hazards to consumers.
C. Pesticide toxicity classification
The WHO (World Health Organization) has classified pesticides based on their
toxicity. Pesticide classes depend on how hazardous they are to humans:
• EXTREMELY HAZARDOUS (Class Ia): Pesticide formulations with, for example,
the active ingredients parathion-methyl, mevinphos, alachlor.
• HIGHLY HAZARDOUS: (Class Ib) Pesticide formulations such as those containing
the active ingredients methamidophos, edifenphos, dichlorvos, monocrotophos, or
methomyl.
• MODERATELY HAZARDOUS (Class II): Pesticide formulations with the active
ingredients ofatox, dimethoate, cypermethrin, fenvalerate, deltamethrin,
fenobucarb, cartap, fipronil, endosulfan, fluvalinate and paraquat.
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• SLIGHTLY HAZARDOUS (Class III): Pesticides with the active ingredients
trichlorfon, dicofol.
• UNLIKELY TO PRESENT ACUTE HAZARD IN NORMAL USE (Class IV):
Pesticide formulations unlikely to present acute hazard in normal use such as
those with the active ingredients zineb, benomyl and maneb.
D. How to apply pesticides
The effectiveness of a pesticide is highly dependent upon:
• Appropriate target: The pesticides used should be appropriate for the organisms
they are targeting. For example, to control leafminer attack, an insecticide able to
kill larvae inside the leaves should be used. A list of target living organisms can be
seen on the labels of the packaging.
• Appropriate timing: Timing should be based on the behavior of the targeted pest
and the weather at the time of application. If a pest is active in the morning, it is
best to apply the pesticide in the morning too. Weather, especially rain and sun
shine, can be very influential. Many pesticide types cannot resist washing by
rainwater and long hours of sunshine.
• Appropriate quantities: Recommended quantities are shown on the pesticide
packaging. These should be adhered to, as inappropriate quantities will cause
negative effects, such as ineffectiveness and build-up of resistance.
• Appropriate application methods: Pesticides should not be mixed when they are
applied, as some will counteract each other and reduce toxicity to target
organisms.
The amount of pesticide the spraying equipment releases can also influence
effectiveness. Generally, a finer spray is better because the smaller droplets will
adhere better to the plants and the bodies of targeted pests, provide better coverage
and will reduce the amount of water and pesticide required. The problem of a finer
spray is that it can be blown away by the wind.
When spraying, consider wind direction to prevent poisoning from becoming covered
with pesticide.
E. Resistance and resurgence
Evidence shows that the more farmers use pesticides, the more problems arise with
pests and diseases. Examples of this are increasing numbers of brown plant hoppers
on rice crops and leafminer flies on potatoes as a result of insecticide use.
The processes causing increased numbers of insects after insecticide application are
as follows:
• Insecticide causes resistance in insect pests. In a population, each individual
insect reacts differently to the insecticide applied. Sensitive ones will die when
coming into contact with insecticide. However, somewhat resistant insects will
survive. When the survivors reproduce, their offspring will be resistant, too.
Through selection the population will be more and more resistant until the
insecticide is totally ineffective. The same process applies to fungi and fungicides.
• Insecticides kill natural enemies. Natural enemies, particularly parasitoids, are
generally more sensitive to insecticide than insect pest. Without natural enemies,
pest insect populations can increase rapidly. This process is called resurgence.
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F. Pesticide hazards to humans and the environment
The dangers of pesticides to humans and the environment are:
• Poisoning in humans: Farmers commonly spray pesticides using no or limited
form of protection, without covering their noses and mouths, or wearing longsleeved
clothes and long trousers. Poison that sticks to the skin and is breathed in
through the nose, can poison farmers. Blood tests conducted among vegetable
farmers showed that all the farmers tested had traces of pesticide in their blood.
Pesticide poisoning does not only cause death, but can cause skin diseases,
nausea, weakness, headaches, convulsions etc. Some chronic symptoms include
cancer, allergies, abnormal blood pressure, etc.
• Polluted produce: Poisons, particularly systemic poisons can enter all parts of
potato plants, including tubers. These poisons remain there for a long time, and
when potatoes are consumed, the poison can enter the body of the person eating
them. An accumulation of these poisons can affect health. International markets
have banned vegetable produce with too high pesticide residues.
• Kills living creatures other than those targeted: Pesticides applied in the field do
not only kill targeted pests/diseases, but can also kill beneficial insects such as
honeybees, as well as livestock.
• Water and air pollution: Water is polluted and poisoned by discarded packaging
and bottles being left lying around in the field, by cleaning spraying equipment in
rivers, and also by rain water flowing from sprayed fields. This is extremely
hazardous to farmers in mountainous regions as they commonly use river water
for their daily consumption needs.
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7 MAJOR POTATO PESTS
7.1 Leafminer fly
The potato leafminer fly (Lyriomyza huidobrensis) originates from North America, and
was accidentally introduced into Southeast Asia in the 1990s on ornamental plants.
This pest affects numerous crops and weeds, and has more than 40 species of host
plants, including potatoes, kidney beans, green beans, okra, Indian mustard, and
several weeds.
Farmers control this pest mainly with insecticides, but this has been ineffective and
has actually increased their numbers. Leafminer flies that are accidentally introduced
are generally already resistant to insecticides.
Life cycle
The leafminer fly reproduces by laying eggs. Its life
cycle is divided into egg, larval, pupal and adult fly Egg
Fly
development stages:
• Eggs - Laid inside leaves, they are very small and
clear in color. Larvae hatch after about two or three
days.
• Larvae – These remain inside leaves. They are
very small and have no legs so cannot move from
Larva
one leaf to another. The larval stage lasts around
6-12 days.
• Pupae – These are formed in the ground or inside
Pupa
leaves. On potato plants, pupae usually fall to the
ground. The pupal stage lasts around 14-16 days.
• Adult flies – These are extremely small at 2-4 mm in length, black in color with two
yellow spots on their backs. They are most active in the morning from 7:00 to 9:00
and in the afternoon from 16:00 to 18:00. Adult flies produce an average of 166
eggs per female. They are attracted to the color yellow.
Damage symptoms
The leafminer fly damages plants during its larval and adult stages mainly on the
lower third of plants. Larvae begin eating the insides of leaves immediately after
hatching, and bore mines inside them. In instances of severe infestation, all that is
left of leaves is their upper and lower skins. Affected leaves become dry and drop off
the plant. Adult flies puncture holes in leaves in order to lay eggs and feed on plant
juices.
If this pest infests a crop during the early plant growth stage, potato yield can be
reduced by up to 70%.
Management
Methods for managing this pest are:
• Clearing and destroying non-crop host plants and residues.
• Planting trap crops such as green beans and pulses at the right time and in the
correct quantities.
• Hilling up at the appropriate time (four to six weeks after planting). This is to bury
and kill the pupae that have fallen to the ground.
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• Balancing fertilizer use to produce healthy plants that can protect themselves from
leafminer flies by ejecting eggs from inside their leaves.
• Rotating with crops that do not host this pest such as maize or sweet potato.
• Protecting natural enemies by not using insecticides as these affect natural
enemies more than leafminer flies.
• Collecting leaves infested with leafminer flies and putting them in parasitoid
release cages.
• Attracting parasitoids and increase longevity by planting nectar-producing flowers
around the field.
• Using organic fertilizer in abundant quantities as predators, for example the
predatory fly Coenosa, breed in organic matter. This will provide them with more
space to breed and develop in larger numbers.
• Putting up stakes as places for predators to wait and view their prey before
striking.
• Place yellow sticky traps for monitoring of adult flies and their natural enemies.
Observation methodology
You can observe leafminer flies directly or by using yellow traps. With direct
observation, look out for plant damage and the presence of adult flies. It is best to do
this in the early morning or late afternoon when the flies are most active. Indirect
observation can be done by using sticky yellow traps, which when put up in high
density can contribute to fly control.
7.2 Potato tuber moth
Potato tuber moths (mainly Phthoremaea operculella) are found both in storage
areas and in fields. Farmers do not usually consider them to be an important pest in
seed tuber production because affected tubers will still grow when planted.
Life cycle
Potato tuber moths lay eggs. Their life cycle is divided into
egg, larval, pupal and adult moth stages, and lasts for
around 20-30 days:
Moth
• Eggs are very small and usually laid on tubers, on the
underside of leaves, on storage sacks, on the ground
Pupa
Egg
or on waste close to tubers. Eggs hatch after five days.
• The resulting larvae make holes in tubers and leaves.
They bore into the eyes of tubers and grow for about
Larva
14 days.
• Pupae are covered in fine hairs and are found on dry leaves, on the ground, on
potato eyes, on the walls of storage areas and on sacks. The pupal stage lasts for
eight days.
• Adult moths have blackish brown colored front wings. They are active at night and
are attracted to light. During the day they hide under sacks or under piles of tubers
stored in the storage area. Adults live for around 10-15 days.
Damage symptoms
Potato tuber moths affect both tubers and foliage. Larvae eat their way inside tubers
either in the field or the storage area. However, severe infestation generally occurs in
storage. Larvae feces can be seen near boreholes.
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On foliage, larvae attack the stems and leaves of potato plants. They enter leaves,
eat the inside and leave only a dried up outer skin. Severe infestation occurs in same
areas, but yield loss is generally limited.
Management
Ways to manage potato tuber moth:
• Using healthy seed tubers – Affected tubers with eggs, larvae or pupae still inside
them can become the source of infestation in the following crop. You should sort
tubers before storing them or planting them in the field. You should destroy
affected tubers by burning or burying them in the ground.
• Mechanical control – Either in the storage area or in the field by removing and
destroying affected tubers and leaves.
• Cultivation practices – You can prevent adult moths from laying eggs on tubers in
the field by hilling up, irrigating and covering over those tubers appearing on the
surface of the soil. Cutting back plants at 80 DAP can prevent larvae on the
foliage from moving into the tubers.
• Crop rotation – Crop rotation is a good way of breaking the cycle of reproduction
when populations are large and causing a lot of damage. The population will be a
lot lower the next time a crop is planted.
• Using sex pheromones – Sex pheromones are useful for observing populations,
but can also be used for management when combined with other management
practices.
• Preserving natural enemies – Create favorable conditions for predators and
parasitic wasps. Further research is necessary to look at the potential of these
natural enemies to reduce populations.
• Using Granulosis virus (GV) – Some research institutes produce a formulation of
GV, which can be an effective means for controlling potato tuber moth larvae,
particularly in storage areas. Tubers for storage are cleaned first and then coated
with GV powder and prepared for storage. Farmers can produce GV themselves
cheaply and easily, but prior training is needed.
• Using Lantana camara – You can also cover stored tubers over with Lantana
camara leaves.
Observation methodology
You can make observations of larvae and adult moths. Observe larvae in the storage
area by removing holed tubers and cutting them in half. Observe larvae in the field by
looking for leaves showing signs of damage and opening them up. Observe presence
of adult moths by using sex pheromones, which attract male insects.
7.3 Aphid
Aphids are always found on potato crops, from when shoots emerge up until the end
of the vegetative growth stage. They are small, soft and green-yellow in color. Some
of the adults have wings and some have not. These pests always group together,
especially on those parts of plants shaded from direct sunlight.
Life cycle
Aphids reproduce in two ways: by laying eggs and
having live young. Which birth process is used
depends on environmental conditions and the
availability of food. When food is plentiful, aphids give
birth to live young. Populations develop quickly as this
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pest has many young, a short lifespan and pre-adult insects can also give birth.
Eggs hatch after three or four days. Young aphids, called nymphs, need five to eight
days to become adults.
Damage symptoms
• Direct damage: Aphids damage plants by puncturing them and sucking their
juices. They damage the young and soft parts of plants, such as new leaves and
shoots. Signs of damage are leaves not opening properly and being smaller in
size. Severe infestation can cause shoots to wilt and dry out.
• Indirect damage: Aphids have wings and can move from plant to plant spreading
viral diseases, picked up from infected plants.
• Aphids secrete a sugary liquid that stimulates black sooty mold growth. It can
cover the surface of leaves which affects the way they absorb sunlight.
Management
Aphids have many natural enemies: parasitoids, predators and pathogens. Potential
predators include ladybird beetles, both adult and grub and,syrphid larvae all of
which are commonly found in potato fields not sprayed with insecticides. A common
parasitoid is Dieretella spp, easily recognized by the presence of mummified aphids
in the colony. Aphids can also be killed by fungal infections and dead aphids
blanketed in a white powder (the spores of the fungus that has killed them) are often
found in fields that are not sprayed with insecticides.
Observation methodology
It is best to observe aphids in the morning by opening new leaf shoots or observing
the undersides of young leaves. Another way to detect their presence is by looking
for ants on the potato plants as they feed on the sugars secreted by aphids.
7.4 Thrips
Thrips (Thrips spp) are very small, have elongated
abdomens and are yellowish or blackish in color.
Although the adults have wings, these insect pests do
not usually fly. They are often found on potato plants
throughout all growth stages, from sprout development
to tuber maturation.
Life cycle
Thrips reproduce by laying eggs. Nymphs emerge from
the eggs. It takes between 7 and 12 days to develop
from eggs into adult thrips.
Damage symptoms
As with aphids, thrips also cause direct and indirect damage:
• Direct damage: Thrips damage the undersides of leaves by sucking their juices.
They damage young and soft parts of plants such as new leaves and shoots. As a
result, leaves curl downwards and change to a blackish- silver color. Severe
infestation causes young leaves to wilt and dry out.
• Indirect damage: Thrips can carry and spread viral diseases.
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Management
Thrips can be controlled by:
• Natural enemies – Particularly generalist predators can regulate thrips populations
• Sufficient watering – Thrips thrive in dry conditions and watering will increase
moisture and inhibit their development.
• Using black silver mulch – Light reflected from the silvery surface illuminating the
undersides of leaves can repel thrips.
Observation methodology
It is best to observe thrips in the morning by looking directly at the undersides of
young leaves.
7.5 Cutworm
Cutworms (Agrotis spp.) can be found in potato fields from when they are tilled up
until crops are ready for harvesting. Cutworms not only damage potato plants, but
also affect almost all types of plants including weeds.
Life cycle
Cutworms reproduce by laying eggs. Their life cycle
includes eggs, larvae, pupae and moths. It takes up to
36 days for them to develop from eggs to adult insects.
The various stages display the following characteristics:
• Eggs are laid on the surface of the soil, but are very
difficult to see. On average, each female adult insect
produces about 970 eggs, with a maximum of 2,370.
• Larvae live in the soil and are either yellow or
blackish- green in color. They have striped markings
running down the sides of their bodies. It is during
this stage of their life cycle that cutworms affect
potato plants.
• Pupae are brown, about 1.5 to 2.0 cm in length and are usually found in or on
piles of leaf mould.
• Adult insects are black and white colored moths. They are not pests, as they feed
on nectar.
Damage symptoms
These pests damage plants and tubers, especially after dark. They attack young
plants by severing their stems, pulling all parts of the plant into the ground and
devouring them. Plants with severed stems have difficulty growing again. This pest
can cause serious damage; particularly when crops are at 25 – 35 DAP.
Signs of damage on tubers are boreholes larger than those made by potato tuber
moths.
Management
Management practices for this pest include:
• Manual control – Collecting larvae when tilling soil, planting, weeding and hilling
up. Any larvae collected should be destroyed by burning or fed to chickens. You
can collect larvae by dismantling the soil around affected plants.
• Attracting cutworm larvae using rice bran – Heaps of rice bran should be placed in
several places in the late afternoon. Cutworm larvae are attracted to rice bran
(and vegetable residues, such as chopped cabbage leaves) and will usually come
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to eat them. They can be removed from the rice bran the following day and
destroyed.
• Biofumigation- The use of biofumigation derived from brassica residues could be
considered on soils heavily infested with cutworms.
• Flooding field prior to planting- Where/whenever possible farmers can consider
temporarily flooding fields, particularly on severely infested fields.
Observation methodology
You can make observations in the morning, by looking for signs of cutworm damage
and dismantling soil around affected plants. However, it is sometimes difficult to find
the remains of affected plants as they are pulled into the ground. It is relatively easy
to identify the larvae of the cutworm; when picked up, the caterpillar will curve itself in
a characteristic C-shape.
7.6 White grub
Many plant species host this pest. White grubs live in loose soil, leaf mould or
manure. This pest attacks potato tubers. Affected tubers can still be sold or
consumed by farmers themselves.
Life cycle
White grubs are the larval form of beetles. They are
large reaching 2-3 cm in length, are shaped like the
letter C, and have three pairs of legs on their thorax.
Their heads are hard and ruddy-brown in color, and they
have strong mandibles. This insect develops by laying
eggs. White grubs develop for up to seven months, and
then have a rest period of 40 days after which they
pupate and remain in that form for two months.
Damage symptoms
Tubers damaged by white grubs have irregular holes. More than two holes are often
found in one tuber. These holes are not so deep, as white grubs do not enter and live
inside tubers. Severe infestations usually occur in fields previously covered with
grasses.
Management
This pest can be managed by:
• Collecting larvae when tilling soil, planting, weeding and hilling up. Any larvae
collected should be destroyed by fire or fed to chicken.
• Avoiding to use uncomposted organic fertilizer, as it is a suitable breeding ground
for this pest.
• Avoiding to plant potatoes in fields that were previously covered with grasses. If
there is no choice, then you should plant several weeks after tilling the soil.
• Biofumigation- The use of biofumigation derived from brassica residues could be
considered on soils heavily infested with cutworms.
• Flooding field prior to planting- Where/whenever possible farmers can consider
temporarily flooding fields, particularly on severely infested fields.
Observation methodology
It is difficult to observe this pest, as it lives in the soil. Some plants can be pulled up
at 70-75 DAP to look for signs of damage.
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7.7 Mole cricket
Mole crickets attack numerous types of plants. They are active at night and adult
insects are attracted to light.
Life cycle
They reproduce by laying eggs. Their life cycle is divided into the egg, pre-adult and
adult stages. Pre-adult insects are similar to adults, but have no wings. Adults are
similar to crickets, but have large, strong front legs, which they use for digging into
the ground. All of their development stages take place in the ground.
Damage symptoms
Economic losses arise from damage to potato tubers. Affected tubers are full of holes
eaten out by these insects. They cause more damage in the dry than in the rainy
season.
Management
You can control mole crickets by clearing plant remnants from the field and using well
composted organic fertilizer.
Observation methodology
This pest is active under the ground and therefore hard to observe.
7.8 Whitefly
Whiteflies not only affect potato plants but also other vegetable and grain crops. This
pest has never caused a potato crop to fail.
Life cycle
Their life cycle is divided into egg, pre-adult and adult stages. Generally, it is easy to
find adult whiteflies in potato fields. They are small in size (1-2 mm long), have wide
wings, are white in color and are usually found on the underside of leaves.
Damage symptoms
Whiteflies damage plants by sucking their juices. Affected leaves become weak and
eventually dry out. Whiteflies secrete sugars that stimulate growth of black mold,
which affects the way leaves absorb sunlight.
Management
Conserve natural enemies and avoid the use of insecticides. Insecticide use actually
triggers the resurgence of this pest.
Observation methodology
You can observe white flies by looking at the undersides of leaves.
7.9 Spider mite
Spider mites are not actually insects but still belong to the arthropod family. They are
small (about 0.5 mm in length), have four pairs of legs and are yellow or reddish in
color.
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Lifecycle
The stages of the spider mite’s lifecycle are egg, pre-adult
and adult. Eggs hatch after three or four days. In both their
pre-adult and adult stages spider mites are similar to spiders.
They are pests during both pre-adult and adult stages. The
pre-adult stage lasts for about 6-10 days. Adults can lay 10-
15 eggs a day.
Damage symptoms
This pest damages young parts of plants by puncturing them and sucking the juices.
Affected leaves look spotty, while affected shoots curl up and do not grow. In severe
infestations, leaves and shoots dry out and die.
Management
Management techniques for controlling spider mites:
• Conserve natural enemies. Spider mites have many natural enemies, including
predators (e.g. predatory mites), parasitoids and pathogens.
• Avoid warm dry environmental conditions. Make sure you water plants, especially
when you plant them in the dry season.
Observation methodology
It is best to make observations in the morning, by looking directly at the undersides of
leaves or at new shoots.
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7.10 Picture of major potato pests
Lyriomyza huidobrensis – adult leafminer fly
Leafminer fly damage
Potato tuber moths (2 species) PTM larva in stem PTM damage on leaves
PTM damage in tuber
Thrips on underside of the leave
Aphids on underside of leaves
Whitefly adults
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Cutworms in tubers
Cutworms on leaves
Mite adults
Mite damage
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8.
MAJOR NATURAL ENEMIES OF POTATO PESTS
8 MAJOR NATURAL ENEMIES OF
POTATO PESTS
8.1 Predators
8.1.1 Ladybird
There are two kinds of ladybirds; dull-colored ladybirds that eat plant and shiny ones
that are predators of other insects. Numerous species of predatory ladybird can be
found on potato crops. You can differentiate between ladybirds by the color of their
hard wings. There are red ladybirds, yellow ladybirds and speckled ladybirds. Both
pre-adult and adult insects are equally effective preying and at controlling pests.
They particularly prey on aphids, thrips and mites. Pre-adult insects are more
voracious, and can eat more than 30 preys in a day. They kill and eat all parts of their
prey.
Eggs Larva Pupa Adult
8.1.2 Ground and rove beetles
Beetles are hard-bodied flying insects. There are many
species in this insect group. Grubs and adults of the
ground beetle can prey on around three to five insects a
day. They prey on insect larvae, aphids, thrips and mites.
Rove beetles, which are black and red in color and have
short outer wings, are very active and can be seen
running around on the crop foliage hunting for eggs,
larvae and small insects.
Ground beetle
Rove beetle
8.1.3 Hoverfly or Syrphids
These flies are found on all crops and include a variety of species. Adult insects tend
to hover or fly in one spot, hence the name hoverfly. Pre-adult insects are predatory,
commonly referred to as syrphids, while adults feed on nectar.
The larvae of these insects have extremely small heads,
with hooked mouthparts; they have no legs, and soft
translucent bodies. You can find them preying on groups
of aphids by puncturing them with their hooks and
sucking out their fluids. These predators can prey on
around 8-22 insects a day.
Adult insects are brightly colored with different species having different colorations.
They have one pair of wings and move around very actively.
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8.1.4 Spider
Spiders have great potential as predators on potato crops. Apart
from their many species, spiders also proliferate over large
areas. Commonly found spiders on potato crops are hunting
spiders, wolf spiders, jumping spiders, orb web spiders and longjawed
spiders. Some spin webs to trap their prey, while others
pursue their victims. Some spiders live on potato plants, and
others live on the surface soil.
Both pre-adult and adult spiders are predatory. Spiders prey on
either flying or crawling insect species that move around actively.
Their predatory capacity depends on the spider species and type
these could be butterflies, moths, grasshoppers, crickets, flies,
etc.
8.1.5 Praying mantis
Praying mantises are rarely found on potato crops. These predators not only prey on
pests, but also on other predatory insects or parasitoids. They prey on flies, bees,
butterflies and small spiders.
Pre-adult and adult praying mantises are predatory. They use
their strong front legs to capture their prey. These predators do
not actively pursue their prey, but wait and catch those insects
that come too close. Because of their wide range of prey,
these predators are not so important in regulating numbers of
insect pests on potato crops.
8.1.6 Earwig
Earwigs move around actively on the surface of the soil. They have a
pair of pincers at the back of their abdomens. These predators vary
greatly in color and size. They are regularly found in dry regions, hunt at
night and hide in the soil during the day. Adult insects can live for three
to five months. These predators prey on aphids, thrips and several kinds
of insect larvae.
8.1.7 Predatory fly
Predatory flies (or killer flies) look similar to houseflies but are smaller in size at
around 0.4 - 0.6 cm in length. They are black with abdomens that narrow towards the
end and prey on aphids, thrips, leafminer flies, etc.
Predatory flies (e.g., Coenosa spp.) are often found preying on other insects in
potato fields. Adult flies actively hunt their prey, which may be in the air or settled on
plants. They grasp their prey with their two front legs, and then suck out their juices
until their victims die. Before striking, these flies
usually wait on stakes or the higher parts of plants to
spot their prey. They can prey on between 5-10
insects a day. Their larvae develop well in soils rich in
organic matter.
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8.1.8 Other predators
Other predators found in potato fields are dragonflies, crickets and red ants. These
insects are highly abundant on potato crops that have not been sprayed with
insecticides, and are suitably effective at controlling insect pest numbers. Predatory
ability depends on the species and development stage of the predator and its prey.
8.2 Parasitoids
8.2.1 Parasitoids of leafminer fly
A. Hemiptarsenus varicornis
Adult insects are a kind of parasitic wasp. They have blue-green
metallic bodies measuring 1.3-1.2 mm in length and have two
pairs of wings. These parasitoids are commonly found on potato
crops. This parasitoid specifically parasitizes leafminer flies
when they are still in their larval form. The wasp lays eggs on
the leafminer larva. After hatching, the parasitoid larva lives on
the leafminer fly larva by sucking its body fluids. Host larvae
growth is stunted and they often die. On potato crops, rates of
parasitism can reach 70%, albeit mostly too late in the season
after a lot of damage has already been done. This parasitoid is
not that effective at controlling quantities of leafminer flies by
itself, but is complementary in a diverse natural enemy complex
in the potato field.
Male
Female
B. Opius sp.
Adult Opius wasps have black bodies, two pairs of wings
and jointed antennae. Although it is not so common, this
parasitoid is generally more effective than Hemiptarsenus.
It also parasitizes flies in their larval and pupal stages. The
larva and cocoons of this parasitoid live inside leafminer fly
larvae and pupae. Parasitized larvae and pupae will die.
Intensive use of insecticides on potato crops will cause
very low levels of parasitism.
C. Gronotoma sp.
Adult insects have black bodies and jointed antennae that look
like beads. This insect solely parasitizes leafminer fly larvae.
Parasitoid larvae live inside the bodies of leafminer fly larvae.
Parasitized leafminer larvae can pupate, but will not develop
into adult flies.
8.2.2 Parasitoids of other potato pests
Other parasitoids are found not only on leafminer flies,
but also on other insect pests, such as aphids, cluster
caterpillars, potato tuber moth larvae or cabbage looper
larvae. The appearance of mummified aphids is a clear
indication of the presence of the common parasitoid,
Dieretella spp. Another way to determine whether
parasitoids are present is to remove insect pest larvae
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from the field and keep them in an enclosure for several days. Observe what insects
emerge, the insect pest or a parasitic wasp or fly.
8.3 Pathogens
8.3.1 Granulosis Virus (GV)
GV is a virus that can infect potato tuber moth larvae and is effective for managing
this pest on potatoes in storage. Tuber moth larvae infected with GV are apparent
from their slow movement, smaller bodies, their milk-white color, and ultimate death.
Dead larvae will break open and exude slime.
Farmers can produce GV themselves and use it in storage areas. The steps in
producing GV are (1) rearing potato tuber moths as hosts, (2) propagating GV, and
(3) formulating GV for use.
A. Propagating potato tuber moths as media for producing GV
• Rear potato tuber moth larvae collected from the field in propagation boxes,
providing them with potatoes to feed on. To make it easier for the larvae to enter
the potatoes, cut them into 1-1.5 cm thick slices and make holes in these slices
with a nail.
• Check and clean the box every day to make sure the larvae do not die from fungal
or bacterial infection.
• When larvae are ready to pupate, move them to another box lined with a 2-3 cm
layer of sterile soil to allow pupation.
• Harvest the pupae when you are sure all the larvae have pupated.
• Move the pupae into plastic boxes covered with gauze.
• When the pupae become moths, smear a 10% concentration of honey on the
walls of the box.
• Place a thick layer of tissue paper on the box top for the moths to lay their eggs
on.
• Collect eggs every day and label them showing the date they were collected.
• Place eggs in a refrigerator or a cool place for several days to stop them from
hatching too soon.
• The next stage is hatching the eggs to propagate larvae or produce GV.
B. GV propagation
• The virus can be sourced from the field or supplied by a
laboratory.
• Crush up 20 larvae infected with the virus and add a
liter of water and some emulsifier compound.
• Immerse potatoes or potato tuber moth eggs into the
mixture for one minute, and then allow them to air dry.
The virus will stick to the surface of the tubers or potato
tuber moth eggshells.
• Place the tubers and the eggs into the propagation box.
• To treat tubers, eggs or newly hatched potato tuber
moth larvae, place them into a storage box that already
contains a tuber covered with GV. To treat eggs, dip
them into a GV solution and then put them with a potato
that has not been treated with GV.
• After 2-10 days, harvest infected larvae for use as a
a. Collect potato tuber moth
larvae infected with GV
b. Isolate larvae infected with
GV
c. Store them in a cold place
d. Grind them up
e. Mix GV with water and dip
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biological insecticide or for the next propagation. It is
best to remove larvae when they have just died and
their bodies are still intact.
• Keep larvae infected with GV in a refrigerator at 4-7°C.
tubers in solution
GV formulation
• Crush up 20 infected larvae and add 1 liter of water and some emulsifier.
• Add 1 kg talc (magnesium silicate), stir thoroughly and allow the mixture to air dry
for several days in shallow trays.
• The formulation is ready for application when storing tubers in the storage areas.
C. Applying GV at storage
• Apply the GV formulation before storing tubers. You will need 5 kg of GV
formulation for every ton of tubers.
• Place GV formulation into a sack(amount according to recommended dose and
volume of sack). Put the tubers for storage into the sack and shake it until you
think all the tubers are evenly coated with GV formulation.
• The coated tubers can then be put into storage.
8.3.2 Bacillus thuringiensis (Bt)
Bt is found naturally in soil and plants. There are numerous strains of Bt capable of
infecting various insect types including larvae and beetles that can affect potatoes. Bt
is now available in commercial formulations in farming supplies shops. Example of
commercial formulations of Bt are Thuricide, Dipel, and Delfin.
Bt poisons and kills insects when they eat it. It is best to apply Bt directly to the parts
of plants being eaten by pests. Apply Bt in the late afternoon as Bt-toxins are easily
inactivated by direct sunlight. After application, the insect will die only after 2-3 days,
but will stop eating very soon.
8.3.3 Nematodes
Nematodes (tiny worms) can be a component in biological control as they can attack
and kill pests. One insect susceptible to nematodes is the leafminer fly in its pre-adult
and adult forms. Various species of nematodes, both those in the ground and on
plants, can infect leafminer flies. They infect them by entering their bodies, growing
inside them and eating their bodies from the inside. Affected flies will eventually die.
8.3.4 Fungal pathogens
There are many types of fungal pathogens that can infect insects. Some examples
are Beauveria bassiana and Metarhizium anisopliae. Collecting diseased insects and
observing their symptoms will provide a lot of information about these pathogens that
can be developed as agents of control. Some commercial formulations are currently
available on the market.
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DISEASE ECOLOGY
9 DISEASE ECOLOGY
9.1 Plant diseases and their causes
Disease is a process in which certain parts of a plant are infected by a
microorganism and cannot function properly. Common causes of diseases are fungi,
bacteria and viruses, which are incredibly small organisms mostly invisible to the
naked eye. Nematodes are also classified under the disease causal agents, although
strictly spoken they are not microorganisms.
The various disease causal agents are characterized as follows:
• Fungi – These are important agents of disease because there are so many kinds.
Fungi have many cells that are formed like threads, and can reproduce from cut
threads or spores. These disease agents can enter plants actively through lesions,
natural holes in plants, be carried by insects, or enter directly through the surface
of a plant. Fungal diseases can spread through water, soil, wind and seeds and on
farming tools. One example of a fungal disease on potato is late blight.
• Bacteria – Bacteria, smaller in size than fungi, are single-celled organisms
capable of reproducing by spores and splitting themselves. They develop
incredibly rapidly in supportive environmental conditions. Bacteria enter plants
passively through lesions and natural cavities or are carried by insects. Diseases
caused by bacteria are bacterial wilt and tuber rot.
• Viruses – Viruses are even smaller than fungi and bacteria. They cannot live
independently and have to be supported by living in the cells of other organisms.
Viruses require plants cells to split and reproduce. Viruses spread from one plant
to another through plant matter (seeds), or carried by insects such as thrips and
white flies.
• Nematodes – Nematodes are classified as animals, are multi-celled and shaped
like tiny worms. They affect plants by puncturing and sucking. Nematodes can
spread actively or passively when carried by soil, water and wind, or on farming
tools and seeds.
Diseases are more difficult to detect than insect pests, because their causes are
extremely small and invisible to the eye. The presence of a disease is only apparent
when symptoms begin to appear.
9.2 Disease management
9.2.1 Principles of disease management
Diseases can break out when there is the following favorable relationship between
the disease causal agent (also called the pathogen), host plants and the
environment:
• The pathogen has the capacity to infect.
• Plants are in a vulnerable condition, due to one or more of the following possible
reasons:
o The plant type and/or variety has no genetic resistance to the disease.
o Plants are at a vulnerable growth stage during which the disease can develop
more easily.
o Plants suffer from poor health as a result of inadequate or unbalanced nutrients
management, which makes them more susceptible.
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• The environment supports the development of the pathogen, for instance:
o Suitable temperature and relative humidity for disease development (often high
temperatures and high humidity).
o The presence of pathogen carriers, such as wind, water, farming tools, insects,
etc.
These three factors are related to each other as depicted in the so-called disease
triangle (see Figure 3).
Disease source
Environment
Host plant
Figure 3: The disease triangle
A disease management strategy can be designed by influencing or changing any one
of these factors of the disease triangle, and hence obstructing disease development,
for instance in the following ways:
Influencing the DISEASE SOURCE by:
• Reducing the presence of diseases in the field by carrying out sanitation,
destroying infected plants, selecting disease-free fields, using clean water for
irrigation and using disease-free seed.
• Breaking the disease chain by rotating crops.
• Using composted organic fertilizer, which increases the quantity and role of living
organisms that can combat diseases, and does not introduce disease causal
agents.
Influencing HOST PLANT health by:
• Using healthy seed to produce a homogeneous, healthy crop.
• Providing balanced fertilization and using composted organic fertilizer to promote
plant health.
• Using resistant varieties where possible.
Influencing and changing ENVIRONMENTAL conditions by:
• Planting potatoes at the end of the rainy season or at the end of the dry season,
so the weather is drier and less suitable for disease agents to develop (note: this
refers to wet tropical highland conditions).
• Making seedbeds higher in the rainy season so the soil is not too wet or moist.
• Adjusting planting density as to reduce humidity around the foliage during the wet
season.
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9.2.2 Biological control
As with insect pests, disease agents also have enemies. These are in the form of
fungi or bacteria, many of which can be found in healthy soil and composted organic
fertilizer. These natural enemies either parasitize on or compete with the plant
pathogen. It is advisable to use large quantities of organic fertilizer when trying to
cultivate healthy potatoes, which provides beneficial microorganisms to the soil to
compete with soil-borne pathogens. Some of these microorganisms are available in
commercial formulations, for instance the antagonist fungus Trichoderma which is a
fungus that eliminates other soil-borne fungi.
9.2.3 Chemical control
It is still hard to remove pesticides for disease management from potato production
systems, particularly fungicides used for controlling late blight. Farmers have been
using pesticides very inappropriately, causing resistance in disease causal agents
and residues on produce, so better management techniques are essential.
Furthermore, pesticides are an environmental pollutant. More information on
fungicide management is provided in the section on late blight (10.2.1) below.
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10 MAJOR POTATO DISEASES
10.1 Bacterial diseases
10.1.1 Bacterial wilt
Bacterial wilt is a disease caused by the bacterium Ralstonia solanacearum. It does
not only infect potatoes, but can also damages plants such as chili, tomato, tobacco
and eggplant, as well as several species of weeds. This disease is extremely
dangerous, especially in regions where potatoes are cultivated intensively. In some
areas, it is the biggest cause of reduced production. Fungicides are sometimes used
by farmers to control this disease, but these are ineffective, because the causal
agent is not a fungus.
Symptoms
The symptoms of bacterial wilt infection can be seen on all parts of infected plants.
They begin to wilt, starting from the tips of the leaves or where the stems branch out,
and then spreading to all parts of the plant. Leaves become yellow at their bases,
then the whole plant wilts and dies. When stems are cut a brown colored ring will be
visible.
Mildly infected tubers will not show any outward signs of disease as symptoms will be
hidden from view. When a tuber is cut in half, black or brown rings will, however, be
visible. If left for a while or squeezed, these rings will exude a thick white fluid. A
further symptom is fluid coming out of tuber eyes. This can be signified by soil
sticking to tuber eyes when crops are harvested. Serious infection causes tubers to
rot.
Source and spread
On potato crops, bacterial wilt originates from:
• Soil - bacterial wilt can survive in soil without a host for several seasons.
• Water.
• Seed tubers.
• Rogue potato plants or other crop or weed plants that can host bacterial wilt.
• Potato plant remnants.
The disease can spread from field to field or from plant to plant in one field via:
• Infected seed.
• Air.
• Water.
• Soil.
• Farming tools.
• Livestock and people.
You must not store tubers infected with bacterial wilt or use them for seed. The
disease will spread rapidly in the warmer temperatures in storage areas, and will
cause tubers to rot. Infected seed can also be a source of the disease in the field.
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Management
Bacterial wilt cannot be controlled with fungicides, and bactericides are seldom
available to farmers and generally very expensive. Management principles for
bacterial wilt are as follows:
• Remove sources of disease from the field by:
o Planting potatoes in soils free from bacterial wilt.
o Using healthy seed not infected with bacterial wilt.
o Rotating potato crops with other non-solanaceous crops. Good practice is to
rotate potatoes with corn or sweetpotato. In fields with serious infections, it is
best to plant non-host plants for more than 2 years, as agents of bacterial wilt
can survive in the ground without host for that amount of time.
o Removing infected plant debris before planting and clearing weeds away
before planting, while plants are growing and at harvesting time.
o Using composted organic fertilizer not infected with bacterial wilt.
o On heavily infested soils, apply brassica residue based biofumigants.
• Inhibit the development and spread of bacterial wilt in the field by:
o Putting dolomitic lime on the soil around infected plants as this increases soil
pH, creating a less favorable environment for the pathogen..
o Carefully managing irrigation in the field by digging channels that allow water to
flow freely from the field. Bacterial wilt will spread rapidly in flooded fields. Also
when watering the field, try to make sure water does not flow over the surface
of the field.
o Using water not contaminated with bacterial wilt to irrigate the crop.
o Cleaning the field by destroying (burning or burying) plants and tubers infected
with bacterial wilt throughout the whole season.
o Cleaning farming tools after use.
Observation methodology
You can begin making field observations for bacterial wilt at 35 DAP by looking at
symptoms on affected plants. Identifying an infection as bacterial wilt can be done by
using the following methods:
• Testing plants with vascular flow test – This will determine whether plants with
symptoms of wilting are infected by bacterial (and not fungal) wilt. Cut 2-3 cm
lengths off stems at the base of plants showing signs of infection. Suspend these
pieces vertically in water and leave for a while. If the plant is infected with bacterial
wilt, milky threads of bacterial ooze will flow from the stem pieces into the water.
• Testing tubers – Cut a sample tuber near its base, leave it for a few minutes, or
squeeze it. If it is infected with bacterial wilt, it will exude a thick white fluid.
• Testing soil with bioassay test – Three-week old tomato seedlings grown on BWfree
substrate and several soil samples suspected of infection are used for testing.
Put the soil samples in pots and water them with clean water. Plant five tomato
seedlings in each pot, and tend them for one or two months. Make observations
by looking at symptoms that appear on each of the plants in the pots. When wilting
appears, test the plants with vascular flow tests. Wilting plants that exude a milky
flow in the vascular flow test are proof that their pots contain infected soil. You can
also do this test to determine if manure contains bacterial wilt.
10.1.2 Blackleg or soft rot
Blackleg or soft rot is a widespread disease caused by the bacterium Erwinia spp.,
which affects stems and tubers particularly in warm and humid regions.
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Symptoms
Blackleg or soft rot can affect potatoes at various stages in their growth. Stem bases
become black, rot and exude slime. Mild attacks in young plants can stunt growth
and cause leaves to yellow and curl upward. Severe infection can cause plants to wilt
and die. Tubers may become infected either in storage or in the field. They rot, but do
not exude the white slime you will find with bacterial wilt. Damage caused by pests,
small worms or harvesting can facilitate infection as the soft rot pathogen can not
infect healthy tissue on its own..
Source and spread
Blackleg or soft rot is spread in nearly the same way as bacterial wilt, i.e. through
seeds, other infected plants, soil and water. It can spread from plant to plant via
water, wind, soil, and seed, and on farming tools or people.
Management
Management of Blackleg or soft rot implies the following practices:
• Avoiding planting in wet or flooded fields.
• Improving irrigation systems to allow water to flow in and out of the field more
easily.
• Using healthy seed not contaminated with the disease,
• Destroying sources of the disease, particularly infected plants.
• Avoiding damage to tubers when weeding, hilling up, harvesting and transporting
harvest produce.
• Harvesting in dry weather conditions.
• Sanitation of the field for the whole season.
10.1.3 Common scab
Common scab, caused by the fungus Streptomyces scabies, is common in fields with
low soil pH. This disease does not cause reduced production, however, it does affect
the appearance, and hence quality, of tubers. These can still fetch almost the same
price as unaffected tubers in local markets, but problems arise when they are sold to
potato processing companies or for export.
Symptoms
Common scab affects potato tubers. Damaged tubers have rough, cracked skins,
with scab-like spots. Severe infections leave potato skins covered with rough black
welts.
Source and spread
Common scab can come from soil, uncomposted manure or seed, and spreads
through contaminated soil, seed and water.
Management
You can control common scab by:
• Avoiding planting in fields with low soil pH, or increasing soil pH by adding lime.
• Using healthy, disease-free seed.
• Rotating potatoes with other non-host crops, such as cabbage or corn, to prevent
the disease from spreading to the following season’s potato crop.
• Avoiding damage to tubers when weeding, hilling up, harvesting and transporting
produce.
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• Destroying infected plants and tubers.
• Managing tuber damaging pests, as damaged tubers are more susceptible to
common scab.
Observation methodology
You should make observations for common scab just prior to and during harvest
time, by taking random tuber samples and inspecting them for symptoms of the
disease.
10.2 Fungal diseases (mold)
10.2.1 Late blight
This is the most important disease, caused by the fungus Phytophthora infestans,
affecting potato crops in the tropical highlands. It regularly causes crop failure,
infecting plants from the tuber initiation stage up until harvest. Severe infections
occur at times of high rainfall, high humidity and low temperatures. Farmers rely
solely on intensive use of fungicides for controlling the disease, but this is mostly
ineffective.
Symptoms
This disease damages leaves, stems and tubers. Affected leaves appear blistered as
if scalded by hot water and eventually rot and dry out. When drying out, leaves turn
brown or black in color. When infections are still active, spots appear on the
undersides of leaves blanketed in what looks like flour. Affected stems begin to
blacken from their tips, and eventually dry out. Severe infections cause all foliage to
rot, dry out and fall to the ground, stems to dry out and plants to die. Affected tubers
display dry brown-colored spots on their skins and flesh. This disease acts very
quickly. If it is not controlled, infected plants will die within two or three days.
Source and spread
Sources of late blight are the air, soil, water, seed and remnants of infected plants. It
spreads very rapidly via air, soil, water and seed. The white powder on the surface of
affected leaves can be carried by the wind and spread the disease to other plants.
Management
This discussion is for farmers who can identify the symptoms of late blight. Late blight
management practices must be based on the relationship between the disease and
factors that influence its development. These factors are as follows:
• The amount of initial inoculum to start the disease off with.
• The rate at which the disease progresses.
• The time since the initiation of the disease
Key practices in late blight management are (1) the use of resistant varieties (if
available), (2) routine observations, and (3) developing management techniques
based on these observations. Varieties with good resistance to this disease are not
yet commonly available to Asian farmers. Therefore, management techniques still
emphasize the more judicious and appropriate use of fungicides. The main aims of
fungicide management when dealing with late blight are:
A. Limiting initial inoculum of the disease in the early plant growth stages.
B. Reducing the spread of the disease.
C. Reducing the duration of infection.
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D. Avoiding serious contamination of the environment.
E. Reducing potato production costs.
The first three points of this list are discussed in more detail below.
A. Limiting initial inoculum of the disease in the early plant growth stages
A.1. Clearing fields of sources of infection
• Using healthy seed not infected with late blight.
• Removing sources of infection by destroying remnants of plants from the previous
crop.
• Destroying infected leaves, plants and tubers.
• Crop rotation.
These techniques are extremely important and provide a high likelihood of success if
farmers plant potatoes in fields that have never been infected with late blight.
However, they can be less effective if surrounding potato crops are infected with late
blight and are not managed using the same techniques. Pathogens are more likely to
spread from other fields on the wind than they are through seed or plant remnants.
A.2. Using resistant plants
Many resistant varieties can reduce instances of early late blight infection. However,
late blight resistant varieties are as yet scarcely available in Asia.
A.3. Fungicide use management
Proper management of fungicide use can protect plants from early infection. But
where, when and how is fungicide use effective?
Fungicide application techniques:
• Treating tubers. Research has shown that the most effective way to use
fungicides is to treat seed. The drawback to treating seed with fungicides is it can
increase the possibility of resistance in the disease itself.
• Treating foliage. The most common form of application is spraying foliage with
fungicide just after plants emerge from the ground. If many plants around the field
are infected with late blight, then newly emerged plants must be sprayed with
fungicide. Any further application should be done based on observation results.
When active spots are found, the plants should be sprayed again.
Initial application:
• The first application is done immediately after you suspect late blight spores are
present in the air. They will be if the surrounding fields are infected. This requires
more thorough observations of farmers’ own, and surrounding fields.
• If you are unsure, assume that spores are present in the air, and you will need to
spray plants soon after they emerge from the ground.
Fungicide types used for initial application:
• Do not mix fungicides in a single application.
• Use systemic fungicide for the initial application. Almost all systemic fungicides
contain adhesive chemicals, so no other adhesive compounds are necessary.
• Four reasons for using systemic fungicide:
o When we think there are pathogens present in the air, we assume that latent
infection has occurred so we must spray plants using systemic fungicide.
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o In their early growth phase, plants grow rapidly and systemic fungicide can
spread into new tissue, thus protecting all parts of plants from early infection of
late blight.
o Spraying during the early growth stage only requires a small amount of
fungicide and minimal cost.
o Systemic fungicides can also control late blight carried by seed potatoes.
How to increase effectiveness of initial fungicide application:
• Try to ensure plants reach their early growth stage simultaneously. Uniform
growth will improve fungicide use effectiveness. You can achieve this by:
o Making good seed beds.
o Planting at a uniform depth.
o Using good quality seeds. Good quality seeds are characterized by uniform
shoot length.
o Using proper equipment - Choose a small spray nozzle, so the liquid sprayed
sticks easily to all parts of the plants.
o Using clean water - It is best not to use dirty water when making fungicide
solutions.
o Fungicides should evenly coat the tops and bottoms of leaves.
Appropriate doses
Recommended dose for most fungicides is 2.5 g fungicide/liter of water. This is a
general recommendation; however, to use appropriate amounts, you should look at
the recommended dose mentioned on the packaging. For example, fungicides with
the active ingredient fluazinam are used in lower doses.
B. Reducing the spread of the disease
There are four factors to disease development capacity:
• The efficiency of agents causing the disease.
• The development stages of the disease from initial infection to producing spores.
• The development level of lesions.
• The capacity to form spores (per unit area).
Farmers should understand the factors influencing the development of this disease,
at least at a conceptual level, because this knowledge is the foundation for
developing management techniques. Modifying one factor will change disease
development. Techniques that can be implemented are described in the following
sections.
B.1. Use of fungicides
Contact fungicides can reduce infection and influence the formation of spores and
the spread of rot on the leaves. With the first application, farmers must decide when,
what with, and how much?
Fungicide application times
This is very difficult to get right, especially in terms of optimizing fungicide use,
because of how it relates to other factors.
• Make regular observations (at least 3 times a week) by looking for symptoms of
the disease. Base observation intervals on your experiences with the way this
disease develops. Appearance of symptoms can be your sign for applying
systemic fungicide.
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• A decision-making system can be used as the basis for applying fungicide. You
can, for example, base your decision to start spraying on how many signs of the
disease appear in the field.
• An application system based on rainfall can be developed based on local
conditions. In Latin America, for instance, the following system was tested:
o If you plant varieties that are not resistant to the disease, you should spray the
crop when rainfall reaches 100 mm after falling for at least 5 days.
o If you plant resistant varieties, you should spray when rainfall reaches 300 mm
after falling for at least 10 days.
Types of fungicide to use
• The theory is that appropriate application methods should be used to ensure
foliage gets a more even coverage of contact fungicides.
• In very wet conditions, you can use an adhesive compound. It is recommended
that you rotate contact and systemic fungicides. In Latin America, it is
recommended to use systemic fungicide 7-10 days after applying contact
fungicide, and contact fungicide 10-14 days after applying systemic fungicide.
Under different condition appropriate intervals should be tested.
• If you find many symptoms of the disease, systemic fungicide is recommended.
Systemic fungicides with a low risk of causing increased resistance in late blight
should be used. These fungicide types can be rotated in 10-15 day intervals.
• The spraying pattern is: systemic – contact – contact – systemic.
Application methods
To improve effectiveness, leaf surfaces should be completely coated when spraying.
Things to pay attention to are:
• Using suitable sprayers – These should still have decent spraying pressure and
appropriate nozzles (yellow code).
• Using clean water with a good pH level. Make sure the water source is disease
free.
• Using appropriate quantities. Check the quantities recommended on the
packaging.
Frequency of application
Systemic fungicides with added adhesives will not wash off for set periods of time, so
farmers can arrange their spraying intervals around the minimum amount of time the
fungicide can last in the field. Spraying intervals will be longer for systemic than for
contact fungicides.
B.2. Management through cultivation techniques
Effective irrigation systems
Fields should not be flooded with water, or be too humid. If possible planting should
be in line with wind direction.
Disposing of infected leaves
Farmers usually use this technique, which is effective for reducing levels of infection,
especially mild infections during the early growth stage of plants.
Plant density (spacing)
This is an important aspect of late blight management. If plants are too close
together, then humidity increases and supports the development of late blight. When
planting in the rainy season, plants should be spaced about 30 cm x 80 cm apart.
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B.3. Using resistant varieties
Using resistant varieties can reduce infection from disease, disease development
levels and spore-forming capacity. However, resistant varieties are currently
unavailable at a commercial level in Asia.
B.4. Improving plant health
Evidence shows that healthy plants can increase their resistance to late blight.
C. Reducing the duration of infection
The shorter the time plants are infected by late blight the better. The following
strategies are for reducing exposure period.
C.1. Using short-duration varieties
Use short-duration varieties so the crop’s critical growth period is not overly long.
C.2. Using seeds that are ready for planting
Seeds should be in optimum condition for planting so they grow quickly, uniformly
and healthily. Storage techniques that optimize light will promote uniform sprouting
so plants grow quickly and are less susceptible to infection from disease.
C.3. Planting healthy seed
Diseases carried by seed can reduce sprouting levels and cause uneven plant
growth.
C.4. Cutting back foliage when tubers reach their optimum size
This technique can help prevent disease moving from foliage to tubers or to
surrounding potato plants. You should destroy the parts you cut from the plants either
by burning or burying them. Plants can be cut back at 80 DAP.
Observation methodology
Observation of the disease must be intensive, beginning when plants emerge from
the ground. It is best to make observations in the morning once every two days,
looking especially at active spots.
10.2.2 Early blight
Early blight caused by the fungus Alternaria solani is found in all potato producing
regions. It is not as important as late blight, because it rarely causes severe damage
or crop failure.
Symptoms
Early blight affects old leaves; its symptoms are dry brown spots, usually bound by
the leaves’ ribs. This disease first becomes apparent during the tuber bulking stage
and develops leading up to harvest.
Source and spread
Sources of infection are contaminated seed and plant remnants. The disease is
spread via wind, water, soil and seeds.
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Management
Management should be carried out when this disease is discovered in the vegetative
growth or tuber initiation stages. Infection in the tuber bulking stage does not affect
harvest quality or yield; therefore, it is not economical to manage the disease during
this stage.
Management techniques for this disease include:
• Removing sources of infection, using healthy seed, destroying contaminated
plants and crop rotation.
• Using good irrigation systems to prevent the disease spreading through water.
• Balanced use of fertilizer to produce healthy plants more resistant to infection from
this disease.
• Cutting back stems at 80 DAP, to prevent the disease spreading to tubers.
10.2.3 Fusarium wilt
As with early blight, this disease, causes by the fungus Fusarium spp, is not a major
problem in potato cultivation in the tropical highlands. Attention should be paid when
planting in warm temperatures or in the dry season.
Symptoms
Fusarium wilt affects potatoes in the field and in storage. Affected plants display
spots and yellowing of leaves. It is more of a problem when it infects tubers in
storage. They become dry and hollow, and concentric circles appear on their skins.
Source and spread
The sources of this disease are contaminated soil and other infected tubers. It
spreads via soil, wind or water.
Management
This disease is generally managed in the storage area, where infection is more
damaging than it is in the field. You can control this disease effectively by sorting and
destroying infected tubers in the storage area.
10.3 Viral diseases
A common problem when cultivating potatoes is reduced yield from one generation to
the next. Farmers often consider the cause to be old and degenerated seed
potatoes.
In fact, this yield reduction is caused by viral infections residing in the seed tubers.
These diseases are very varied and display a multitude of symptoms. It is difficult for
farmers to gain an understanding of viral diseases because:
• Their causal agents are tiny and invisible to the eye.
• Viral infections rarely cause plants to become damaged or die. The symptoms
visible, if any at all, are changes in the shape of plants. Consequently, most
farmers consider viral diseases harmless.
• It is difficult to differentiate between symptoms of one virus and another, as they
are all very similar. Thorough testing calls for equipment and expense well beyond
farmers’ reach.
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Viral diseases have developed from one generation to the next primarily due to
farmers’ habit of basing their seed potato selection on the size of the potatoes alone.
Generally, viral diseases lead to smaller potato tubers being produced.
Consequently, when tubers are sorted and selected for seed, the majority of seed
potatoes chosen are those already infected with viral diseases.
A key factor when obtaining seed from your own field is selecting healthy plants for
parent stock.
Despite variations, management principles are nearly the same for all viral diseases.
Viruses can be controlled by:
• Using virus free seed: It is very risky to select seed potatoes based on size alone,
as plants infected with viral diseases generally produce smaller tubers. Strict
sorting and selection is highly recommended when a part of the harvest will be
used for seed.
• Destroying plants infected with viral diseases: Plants displaying symptoms of viral
diseases must be pulled up, collected and destroyed. Viruses can spread from
one plant to another through vectors, so removing infected plants will also remove
the source of disease for other plants.
• Controlling insects that can spread viral diseases: Generally, sucking insects such
as aphids, thrips, mites and whiteflies can spread viruses. Therefore,
management of these insects can reduce the spread of viral diseases.
• Using plant resistant varieties: This can only be done if available in sufficient
quantities.
• Not using pesticides: Viruses cannot be controlled by any form of pesticide.
10.3.1 Leafroll virus
Potato leafroll virus (PLRV) is an important disease in potato plants, and can cause
reduced yields of up to 90%.
Symptoms
Leaves curl upward and turn pale yellow. If you press them they feel brittle and
fragile. In advanced infections, plant growth becomes stunted, leaf stems stand
upright, leaves curl, tighten and turn pale green. Severe infections cause potato
plants to produce tiny tubers, or prevent them from producing any tubers at all.
Source and Vector
PLRV can be introduced into a potato field by infected seed tubers or by aphids who
act as vector spreading the disease from one field to another.
Observation methodology
Symptoms appear during the early stages of potato growth, so observations should
begin at that time. Make observations by walking along the raised seedbeds and
looking for plants showing symptoms of the disease.
10.3.2 Potato Y virus
Potato Y virus (PVY) is the second most important virus. It can be passed on through
infected tubers or by insects and can reduce yield by up to 80%.
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Symptoms
Leaf surfaces become uneven and brittle, leaves shrink and their ribs turn yellow. In
mild infections, plants often show no signs of disease at all.
Source and Vector
Although the virus can spread with infected seed tubers and mechanical transmission
through tools and plant/tuber handling, PVY is mostly transmitted by aphids who act
as vector spreading the disease from one field to another. Aphids can acquire the
virus within seconds after starting to feed on infected leaves, can transmit the virus
immediately, in a non-persistent manner and usually retain the virus for only several
hours without continued feeding on infected leave material.
Observation methodology
These are the same as for leafroll virus.
10.3.3 Mosaic virus
Symptoms
Yellowy-green stripes appear on leaves infected by the Potato Mosaic Virus (PVM).
Yield can diminish by up to 40%. In mild infections, affected plants display no
symptoms.
Source and Vector
Like other viruses, PVM is caused by using contaminated seed, can be mechanically
transmitted through tools and plant/tuber handling or is carried from other plants by
aphids.
Observation methodology
These are the same as for leafroll virus.
10.4 Diseases caused by nematodes
10.4.1 Root-knot nematode
Root-knot nematodes damage the parts of plants found under the ground, i.e. roots
and tubers. Although this disease is found in many potato producing regions, farmers
do not consider it too economically damaging and consequently pay it little attention.
Nevertheless, these nematodes can reduce tuber quality and can make them more
vulnerable to other diseases. Lesions caused by nematodes facilitate secondary
infections by other diseases in the soil such as tuber rot and scab to get in.
Symptoms
Diseases caused by nematodes vary, but common symptoms of these are:
• Swelling of roots – Nematodes damage and live in the roots of potato plants,
causing them to swell. Swollen roots cannot function normally and affect growth of
the plant above them. In hot conditions, plants damaged by nematodes will wilt.
• Irregular tuber shape – Tubers change shape and lumps appear on their surfaces.
Source and spread
Sources of these diseases are soil and contaminated seed. Nematodes can move
around in the soil with the help of water.
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Management
Root-knot nematodes can be managed by:
• Using healthy seed free from nematodes.
• Balancing fertilizer use to obtain healthy plants less susceptible to nematodes.
• Rotating potato crops with corn or other non-solanaceous crops.
• Biofumigation in case of severely-infested soils
Observation methodology
Pull up wilting plants and observe their roots and tubers. If you find any symptoms
like those explained above, you could conclude that plants have been infected by
nematodes.
10.4.2 Golden cyst nematode
Potato cyst nematodes, probably originating with the potato in South America, are
widely distributed throughout potato producing areas all over the world. Although its
main host is the potato, it can also reproduce on other solanaceous crops such as
tomato and eggplant. There are two main species, the golden (Globodera
rostochiensis) and the pallid (G. pallida) cyst nematode. The golden cyst nematode
was first identified in Indonesia in 2003 and is rapidly spreading.
Life cycle
One life cycle of the golden cyst
nematode is completed with each crop.
Between crops, eggs survive within cysts
in the soil. When a potato plant is growing,
substances exuded by the roots stimulate
the eggs to hatch. Each egg contains a
second-stage juvenile which hatches,
moves from the cyst into the soil and
penetrates a host root just behind the
root-tip. The juvenile establishes a
permanent feeding site in the root and
develops to become an adult.
After reaching the adult stage, males leave the root and move through the soil to find
females. Females remain in the root, expanding and eventually rupturing it,
remaining attached by the head and neck only. After fertilisation, the female
produces 300 to 500 eggs which she retains within her body. The female dies with
the root, but her skin hardens and turns brown while forming a protective cyst for the
eggs.
Symptoms
Potato cyst nematodes do not cause immediate above-ground symptoms. First
symptom is poor growth of plants in one or more spots in the field. These spots
enlarge each year that potatoes are planted in the same field, since cysts remain in
the soil for a long time. Low populations of the nematode may not be noticed but as
the number of nematodes increases, plants become stunted, leaves are smaller and
yellowish and plants dry off early. Plants may show symptoms of water and/or
mineral deficiency stress with yellow leaves and wilting. Yields may be reduced by as
much as 90%, which is the result of smaller tubers. Tuber quality and number of
tubers, however, are not affected.
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Source and spread
The cysts of the nematodes stay in the soil for long periods of time. They can spread
to other fields or other areas through soil on tools, boots and seed tubers.
Management
Of all the crop pests worldwide, the potato cyst nematodes are among the most
difficult pests to control. Once they are established in an area, eradication of the
potato cyst nematodes seems unlikely. The extremely long survival period of cysts in
the soil, which can be over 30 years, limits management options.
The best approach to limiting spread once the potato cyst nematodes are introduced
into an area is to integrate control measures. In particular, crop rotation, resistant
varieties, and biofumigation look promising. Crop rotation, however, requires a cycle
of five to nine years to achieve relatively low populations in the soil that would allow
successful potato production again. Resistant varieties are available in Europe, but
these are not necessarily suitable for tropical highland conditions and need to be
evaluated first. Chemical control is generally not recommendable since it involves
pesticides (nematicides) of high toxicity that kill all living organisms in the soil,
including nematodes, fungi, bacteria, plants and insects. Biofumigation using
brassica residues is a method that should be further explored.
Observation methodology
As with root-knot nematodes, pull up wilting plants and observe their roots and
tubers. Roots of infected plants exhibit very small, white bodies, which are the
immature females that have erupted through the root epidermis. At very high
nematode densities, tubers may become infected, resulting in the appearance of
cysts on their surface.
10.5 Problems caused by environmental factors
10.5.1 Low temperatures
Many of these diseases occur in areas with relatively cool temperatures, such as
basins. Temperatures falling to below 4°C at night cause plants to appear burnt with
leaves eventually drying out. This is caused by a strange property of water, which
expands at temperatures of 4°C and below. When the temperature falls to this level,
water inside the plants will expand and plant tissue will no longer be able to contain
it. Plant tissue will burst and become damaged leaving plants looking burnt.
Management
You can overcome problems with low temperatures by:
• Avoiding planting at times when temperatures are very low,
• If the temperature falls to just above 4ºC, water the plants, as this will prevent the
temperature around them from becoming too cold.
10.5.2 Nutrient deficiencies
Signs of a lack of nutrients are:
• Nitrogen: o Yellowing of leaves.
o Stunted plant growth.
• Phosphorus: o Dwarf plants,
o Foliage turning dark green and curling up.
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• Potassium:
• Calcium:
• Magnesium:
o Plant growth might be stunted, foliage appearing blackish in
color.
o Sometimes black spots are clearly apparent on leaves.
o Shoots drying out and dieing.
o Youngest leaves curling upward.
o Yellowing of leaf ribs.
Management
You can manage these disorders by adding the deficient nutrients as and when
required. When you encounter symptoms such as the ones described above, but
only on a few plants, then you should add more fertilizer only to the affected plants.
10.6 Picture of major potato diseases
Bacterial wilt – wilting of plants
Bacterial wilt – oozing of tuber
Erwinia spp. – blackleg
Erwinia spp. – soft rot
Common scab
Early blight (Alternaria solani) on leaves
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Late blight (Phytophthora infestans) on stem
Late blight on leaves
Late blight on outside of tuber
Late blight inside of tuber
Fusarium dry rot
Fusarium wilt
Potato leafroll virus – rolling of upper leaves
Potato leafroll virus – stunted plants
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Potato virus Y – stunting and yellowing of veins
Potato virus Y – mosaic
Symptoms of mosaic virus
Potato cyst nematode – females attached to roots
Root-knot nematode on roots
Root-knot nematode on tubers
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WEED ECOLOGY
11 WEED ECOLOGY
11.1 Weeds: damaging or beneficial?
Weeds are all the unwanted plants growing on farming land. They compete with the
main crop and considered to produce nothing of any benefit.
Weeds are damaging when:
• They compete with potato plants for nutrients, sunlight, water and living space.
• They require expenditure in their control.
• They become a food source for pests enabling them to thrive, even when there
are no potato plants in the field.
• They host diseases that affect potato plants. Crop rotation will not work if disease
and pest supporting weeds are still present in the field.
Weeds can be beneficial when:
• They serve as green manure providing trace elements and improving soil
structure. Weeds form a fundamental ingredient in making organic fertilizer.
• They form a covering layer protecting soil from sunlight or erosion damage.
• They become a food source for natural enemies. Weeds produce flowers and
nectar that can be an alternative food source for parasitoids.
• They become a food source for livestock.
Whether a weed is damaging or beneficial depends on its species, its density and its
uses. For example, a weed will be extremely useful if it can be used for animal feed.
11.2 Weed types
• Grasses – These have small pointed leaves with jointed stem. Every joint has
roots. These weeds are extremely hardy, and can grow from cut grass or from
seed. They are difficult to control because they can survive even after being
removed from the soil.
• Sedges – Like grasses but without jointed stems. They grow from rhizomes, roots
and seeds. They can even grow from very small pieces of cut root.
• Broad-leaved weeds – These weeds have broad leaves, and sturdy stems with
many branches. They generally grow from seed and are easier to control than
grasses and sedges as they will die when pulled out of the ground.
11.3 Weed management
Weeds have two sides to them; damaging and beneficial. With proper management
we can manipulate their damaging traits and make them beneficial.
Herbicides are used to eradicate all living vegetation in the field, not only to eradicate
weeds. Using herbicides can actually lead to greater losses because:
• Poisoned weeds cannot be used to make organic fertilizer or utilized as animal
feed.
• The poisons herbicides contain last for a long time in the field and can kill or affect
the main crops’ growth.
• Herbicides kill beneficial living organisms in the soil, and reduce soil fertility.
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You can manage weeds in two ways:
• Prevention – Do this before planting the main crop by clearing weeds from the
field when tilling, making raised seedbeds and planting. Collect the weeds, and
make them into organic fertilizer.
• Management when potato crop is growing – You can do this by pulling up weeds
or burying them in the soil. You should do this twice in a season, at 30 and 50
DAP. Be careful when weeding at 50 DAP as tubers are starting to form, and any
damage to potato plant root systems will affect yield and increase susceptibility to
disease.
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HARVEST AND POST-HARVEST MANAGEMENT
12 HARVEST AND POST-HARVEST
MANAGEMENT
12.1 Pruning plants before harvesting
It is recommended to prune plants before harvesting when some of the produce will
be used for seed. Under tropical highland conditions, pruning can be done at 80 DAP
(depending on the variety), by cutting them at the base of their stems. The foliage
can be collected and composted.
Benefits of pruning are:
• To make tubers harden more quickly so they can be harvested sooner. Normally,
you can harvest plants two weeks after pruning.
• To prevent diseases spreading from plant stems to tubers. Viral diseases in
particular will spread to tubers if stems begin to wilt and dry out. The same occurs
to other diseases such as late blight, stem rot and bacterial wilt.
12.2 Harvest time
Each variety has a different preferred harvest age; Atlantic and Columbus, for
instance, need more time before harvesting than Granola, which is ready for harvest
at 100-110 DAP. It is best to harvest in clear, sunny weather, because sunshine will
help tubers to harden and dry more quickly, making it easier to remove excess soil
from their skins.
Harvest time is influenced by potato prices and weather. When prices and weather
are favorable, you can harvest a bit earlier and spread the produce out for a few days
to allow tuber skins to harden. However, when prices and weather are not favorable,
you can delay harvesting. Harvesting in the rain might cause tubers to rot. You
should not delay the harvest for more than 10 days, as delays of any longer will
cause more tubers to become damaged by pests such as mole crickets, or bacterial
diseases and scab. Damaged tubers will fetch a lower selling price.
12.3 Harvesting methods and estimating yield
Harvesting methods affect tuber quality. Potatoes can be harvested in two ways,
directly by hand or by using a hoe. Harvesting by hand takes longer and is more
labor intensive, but will produce good quality, undamaged tubers. Using a hoe is less
time-consuming and labor-intensive, but some tubers will be damaged in the
process.
On loose soil with no grass growth, you can harvest by dismantling potato beds by
hand. Harvested tubers should be put to the side of the dismantled seedbeds so they
are easier to collect. When soil is too hard and is covered with grass, you should dig
up potato beds using a hoe. This can happen when you harvest too late at more than
120 DAP. Dig from the edge of the seedbeds to loosen the soil, then continue
dismantling them by hand. Be careful when loosening the soil so as not to damage
potato tubers.
If the whole produce is going to be sold, then you can harvest all the potatoes in one
go. However, if some of the tubers are for seed, you should harvest them at a
different time from the ware potatoes. You can harvest seed tubers either before or
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after harvesting tubers for consumption by using either positive or negative selection
(see section 4.4.1).
After harvesting, you should sanitize the field, by gathering and destroying harvest
remnants such as plant parts, rotten tubers etc. Post-harvest sanitation is an
important part of controlling various pests and diseases, by removing sources of
contamination for the next crop from the field.
You can estimate potato harvest yield by:
• Weighing several sample tubers taken from randomly selected plants.
• Calculating the average weight of tubers per plant.
• Multiplying that figure by the total number of seeds tubers used (or plants grown)
on the whole field.
For example:
• The tuber weights of five sample plants are 0.9, 0.8, 1.2, 1.0 and 0.5 kg. The
average weight of tubers per plant is:
0.9 + 0.8 + 1.2 + 1.0 + 0.5 = 0.88 kg/plant
5
• The average tuber weight per plant is multiplied by the number of plants in the
whole field to assess the total harvest. For instance, a 1,000 m 2 field contains
2,000 plants. The estimated harvest from the example above is then:
2,000 x 0.88 = 1,760 kg (or 17.6 tons/ha).
• If the number of plants is not known, it can be assessed from the seed rate. For
instance, a farmer planted 100 kg of seed tubers with an average weight of 50 g
per tuber. Number of plants is then:
100 = 2,000 plants
0.05
The estimated total harvest is = 2,000 x 0.88 = 1,760 kg
12.4 Treatment of produce
Harvested tubers are treated as follows:
• Spreading out and drying tubers – Spread out harvested tubers in the field or the
storage area to dry. Harvesting in the dry season enables you to leave the
produce in the field for a long time. In the rainy season, it is best to spread out the
produce in the storage area under lights.
• Sorting – Do this by separating damaged and undamaged tubers and classifying
them according to weight. Gather and destroy any rotten tubers. Tubers damaged
by pests can be sold. Tuber classification varies greatly between countries and
regions. An example of tuber weight classification as used in most parts of
Indonesia is as follows:
o > 80 g/tuber
o 60-80 g/tuber
o 30-60 g/tuber
o < 30 gr.
Tubers weighing 60 g and over are sold, whereas those below 60 g are normally
used for seed.
• Packing – You can do this by using sacks or baskets. Packing must be done
carefully to avoid bruising tubers.
• Transportation to the storage area – Produce can be sold while it is still in the
field, particularly when prices are high and not too many potatoes are available.
When the main harvest takes place, farmers must store harvested tubers in a
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storage area until prices improve. Be careful to avoid any damage when
transporting produce from the field to the storage area.
• Storage – Tubers for consumption are only stored for a few days. If you are
storing them for more than two days, it is best to spread them out on the dry floor
of the storage area to prevent them from rotting.
• Tuber selection for seed – Selection is done on tubers affected by pests and
disease, and tuber size. It is advisable to separate tubers from different weight
classes to make it easier to estimate seed requirements. A one-hectare field
generally requires 1.5 tons of seed tubers weighing 30-60 g/tuber, but only about
1 ton of tubers lighter than 30 g/tuber.
• Storing tubers for seed. See section 4.6 of this manual.
12.5 Marketing and prices
In some areas farmers generally sell potatoes in their fields or in their own villages,
while in other areas traders will come right to villagers’ homes or fields where
potatoes have recently been harvested. An example of a potato marketing channel is
depicted in Figure 4. Prices are usually not too different from one farmer to the next
at the same moment in time, and are mainly influenced by tuber size, quality, smooth
skins, color and whether or not they are damaged. Potato prices can fluctuate greatly
from season to season, though. Farmers should quickly circulate information on
potato prices among themselves to avoid cases of traders taking advantage of them.
Producer farmers
Inter-regional traders
Local traders
Town traders
(central market)
Export market
Retailers
Figure 4: Potato marketing channels
Consumers/Households
12.6 Potato processing
Potatoes can also be processed into various food industry products. The food
processing industry requires increasing numbers of potatoes every year.
Unfortunately, Granola potatoes are not suitable for many of these processed
products, because of their high sugar content. Processed products that can be made
from Granola potatoes are croquettes, potato layer cakes, boiled potatoes, potato
crisps and fried potatoes. Varieties more suitable for processing are Atlantic and
Columbus.
12.7 Analyses of the potato enterprise
An economic analysis provides information on the status of farmers’ businesses and
whether they are making a loss or a profit. This information can provide the basis in
developing cultivation patterns for the following season’s harvest.
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12.
HARVEST AND POST-HARVEST MANAGEMENT
Net income or profit from farming is the amount remaining when you subtract
expenditure from gross income. Both income and expenditure vary from one farmer
to the next.
Income from potato farming:
• Selling potatoes for consumption.
• Selling seed.
• Selling the produce from intercropping.
Types of expenditure vary greatly from one farmer to the next, but generally consist
of the following cost items:
• Purchasing seed.
• Purchasing organic and inorganic fertilizer.
• Purchasing sacks to package harvest produce.
• Purchasing fungicides, insecticides, adhesives etc.
• Labor costs, from tilling to harvesting.
• Transportation costs, when buying inputs.
• Spraying equipment rental costs or depreciation value.
• Other potato enterprise related cost.
Important factors in determining gross income are the amount of tubers that can be
sold for consumption and for seeds, and the prices of those consumption and seed
potatoes. Important factors in calculating expenditure are the number of goods and
services used as well as the size of other expenses. Usually, farmers only count
income and expenditure in cash form. This means ‘wages’ for farming family
members and the value of goods belonging to farmers are not counted. For example,
farmers need not include spraying equipment hire when they already have their own,
but the depreciation value of the sprayer for that particular season should be included
as an expense.
Potato farmers should always record their income and expenditure every planting
season. In the IPM FFS process, farmers learn together how to calculate their
businesses based on the notes they take. IPM FFS participants are given ‘potato
cultivation record’ forms, on which they note down the following things at each
meeting:
• Activities - what work they have done in the study plot.
• Labor – Wages paid for workers and estimated pay for work done by the farming
family.
• Purchase of inputs needed for cultivation – What inputs have been bought, and
how much they cost.
• Comments – All interesting things, such as results of observations, are noted
down.
At the end of the season, the two columns containing amounts of money (labor and
production costs) are added up and recorded on an analysis sheet of the form. When
the produce has been harvested and sold, the gross income is also noted down and
calculated in the analysis sheet, and the farm economic analysis can be done by
calculating the profit.
• Gross income – Total harvest (kg) multiplied by product price (money value per
kg).
• Total expenditure – By adding together the labor costs and production costs.
• Profit – Total expenditure subtracted from total gross income.
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REFERENCES
REFERENCES
BALITSA. 1989. Kentang. Lembang, Indonesia: Balai Penelitian Tanaman Sayuran.
Bennet, W.F. 1996. Nutrient Deficiencies and Toxicities in Crop Plants. Minnesota, USA:
American Phytopathology Society.
Braun, A. R. and M. Shepard. 1997. Lalat Penggorok Daun, Liriomyza huidobrensis
(Leafminer Fly, in Indonesian). Technical Information Bulletin. Bogor, Indonesia:
International Potato Center.
Cisneros F. and N. Mujica. 1999. The leafminer fly in potato: plant reaction and natural
enemies as natural mortality factors. In: Impact on a Changing World, 1997-1998
Program Report. Lima, Peru: International Potato Center.
Department of Primary Industries and Fisheries Queensland. Potato cyst nematode. DPI&F
Note. http://www.dpi.qld.gov.au/horticulture/4848.html
FAO. 2000. Tomato Integrated Pest Management: An Ecological Guide. Bangkok, Thailand:
FAO Inter-Country Program for the Development and Application of Integrated Pest
Management in Vegetable Growing in South and South-East Asia..
Henfling, J.W. 1987. Late Blight of Potato. Technical Information Bulletin 4. Lima, Peru:
International Potato Center.
International Potato Center. 1992. Biological Control of Potato Tuber Moths Using
Phthorimaea Baculovirus. ClP Training Bulletin 2. Lima, Peru: International Potato
Center
International Potato Center. 1996. Major Potato Diseases, Insects and Nematodes. Lima,
Peru: International Potato Center.
Kalshoven, L.G.E. 1981. Pest of Crops in Indonesia. Jakarta, Indonesia: PT Ichtiar Baru-Van
Hoeve.
Oudejans, J.H.M. 1999. Studies on IPM Policies in SE Asia; Two Centuries of Plant
Protection in Indonesia, Malaysia and Thailand. Bachuys Publishers, Leiden.
Rauf, A. and B.M. Shepard. 1999. Leafminers in vegetables in Indonesia: survey of host
crops, species composition, parasitoids and control practices. In: Proceedings
Workshop on Leafminers of Vegetables in Southeast Asia, 2-5 February 1999.
Selangor, Malaysia: CABI Bioscience.
Rich, A.E. 1983. Potato Diseases. Academic Press, New York.
Rowe C. 1993. Potato Health Management. Minnesota, USA: American Phytopathology
Society.
Sahudi A. 1997. Kumpulan Petlap Pengorganisasian dalam Program PHT. Surakarta,
Indonesia: Gita Pertiwi, LPTP, Gema Desa, World Education.
Shepard B.M., A.T. Barrion and J.A. Litsinger. 1987. Helpful insects, spiders and pathogens.
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Soepardi, G. 1983. Sifat dan Ciri Tanah. Bogor, Indonesia: Institut Pertanian Bogor.
Tanada, Y, and H.K. Kaya. 1993. Insect Pathology. Harcourt: Academic Press.
Van de Fliert, E. (1993). Integrated Pest Management: Farmer Field Schools Generate
Sustainable Practices. A Case Study in Central Java Evaluating IPM Training.
Wageningen Agricultural University Papers 93-3. Wageningen: PUDOC, 304 pp.
Van de Fliert, E. and A.R. Braun (1999). Farmer Field School for Integrated Crop
Management of Sweetpotato: Field Guides and Technical Manual. Bogor: International
Potato Center. 197 pp. Published in English, Indonesian, Spanish and Vietnamese.
Van de Fliert, E., Warsito, and A. Lagnaoui (1999). Participatory Needs and Opportunity
Assessment for Potato IPM Development Planning: the Case of Indonesia. Impact on a
changing world. 1997-98 Program Report. Lima, Peru: International Potato Center, p.
171-178.
A HANDBOOK TO THE ECOLOGY AND INTEGRATED MANAGEMENT OF POTATO 81

GLOSSARY
GLOSSARY
Aphid
Bacterial wilt
Bt
CIP
Cluster caterpillar
Common scab
Cutworm
Early blight
FFS
Fusarium dry rot
Golden cyst nematode
Ground beetle
GV
Hoverfly
IPM
Ladybird
Late blight
Leafminer fly
LPTP
Mole cricket
Mosaic viruses
Parasitic nematodes
Parasitoids of leafminers
Pathogenic fungi
Potato leafroll virus
Potato tuber moth
PVY
Root-knot nematode
Root-lesion nematode
Rove beetle
Soft rot
Spider mite
Thrips
WE
White grub
Whitefly
Myzus persicae
Ralstonia solanacearum
Bacillus thuringiensis
International Potato Center
Spodoptera litura
Streptomyces scabies
Agrotis spp.
Alternaria solani
Farmer Field School
Fusarium sp.
Globodera rostochiensis
Carabidae
Granulosis virus
Syrphidae
Integrated Pest Management
Coccinellidae
Phytophthora infestans
Liriomyza huidobrensis
Institute for Rural Technology Development
(“Lembaga Pengembangan Teknologi Pedesaan”)
Gryllotalpa africana
PVX, PVS, PVM and PVA
Steinernema sp., Heterorhabditis sp.
Herriptarsenus varicornis, Opius sp., Gronotomo sp.,
Diglypus sp.
Metarhizium anosiplae, Beauveria bassiana
Potato leafroll virus (PLRV)
Phthorimaea operculella
Potato virus Y
Meloidogyne spp.
Pratylenchus spp.
Staphilinidae
Erwinia spp.
Tetranychus spp.
Frankliniella spp.
World Education
Phyllopaga spp.
Bemisia spp
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